Arc gis tutorial and gis traning manual

INTRODUCTION TO BASICS OF

GEOGRAPHICAL INFORMATION

SYSTEM USING ESRI ARCGIS

DESKTOP GIS for Engineers

ABSTRACT The aim of this exercise is to

familiarize participants with general

GIS terms and the basic

functionalities of ESRI ArcGIS

Desktop.

Kirtan Adhikari College of Science and Technology [email protected]

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Kirtan Adhikari 10-Aug-16

Author’s Note

With the increasing popularity of Geographical System (GIS) in the country and in particular at College of Science

and Technology (CST) GIS enthusiastic people are coming forward to learn and use GIS. Students of CST are opting

for GIS related projects and many faculties of CST aspire to use GIS in their research work. However, due to lack

of in country opportunities, learning GIS is challenging in Bhutan as of now.

Realizing this as an issue I prepared this document attempting to provide means to learn GIS without help from GIS

expert. This document consists of two sections and a mini project at the end. First section explains the functionalities

and usability of GIS for different purposes and second section is designed to enhance knowledge on ArcGIS through

hands on exercises.

Lastly, I am very thankful to CST for providing me ample opportunities, to attend seminars and trainings on GIS. I

am also very thankful to my wife for her endless support, encouragement and spending lot of time in editing these

documents.

This manual may be reproduced in whole or in part and in any form for educational or non-profit purposes without

special permission from the author. No use of this manual may be made for resale or for any other commercial

purpose whatsoever without prior permission in writing from the author.

Author’s Note

With the increasing popularity of Geographical Information System (GIS) in the country and in particular at

College of Science and Technology (CST). GIS enthusiastic people are coming forward to learn and use GIS.

Students of CST are opting for GIS related projects and many faculties of CST aspire to use GIS in their research

work. However, due to lack of in country opportunities, learning GIS is challenging in Bhutan as of now.

Realizing this as an issue I prepared this document attempting to provide means to learn GIS without help from

GIS expert. This document consists of two sections and a mini project at the end. First section explains the

functionalities and usability of GIS for different purposes and second section is designed to enhance knowledge

on ArcGIS through hands on exercises.

Lastly, I am very thankful to CST for providing me ample opportunities, to attend seminars and trainings on GIS.

I am also very thankful to my wife for her endless support, encouragement and spending lot of time in editing

these documents.

This manual may be reproduced in whole or in part and in any form for educational or non-profit

purposes without special permission from the author. No use of this manual may be made for

resale or for any other commercial purpose whatsoever without prior permission in writing from

the author.

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Content

Author’s Note .............................................................................................................................................................. 1

List of Figures ..................................................................................................................................................... 3

Geographical Coordinate System ............................................................................................................................... 4

1. Geographical Coordinate System .................................................................................................................... 4

2. Maps and Projections ...................................................................................................................................... 4

Introduction to GIS .................................................................................................................................................... 5

3. GIS Data model ............................................................................................................................................... 6

4. Geo-Referencing .............................................................................................................................................. 7

4.1 Exercise On Geo-Referencing using ESRI ArcGIS Desktop ................................................................. 7

5. Digitally Representing Geographical data.................................................................................................... 15

5.1 Exercise on Digitization ......................................................................................................................... 16

6. Raster Data Processing (Digital Elevation Model Processing) ................................................................... 20

7. Delineating watersheds ................................................................................................................................. 22

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List of Figures

Figure 1 The Earth ....................................................................................................................................................... 4

Figure 2 The Schematic representation of Map Projection ......................................................................................... 4 Figure 3 Schematic representation of GIS................................................................................................................... 5

Figure 4 Thematic layers in GIS ................................................................................................................................. 5 Figure 5 Vectors Icon (in ArcGIS) .............................................................................................................................. 6 Figure 6 GIS data model.............................................................................................................................................. 6 Figure 7 Step 1 Geo-Referencing ................................................................................................................................ 7 Figure 8 Step 2 Geo-referencing ................................................................................................................................. 8

Figure 9 Map of Bhutan .............................................................................................................................................. 8 Figure 10 Step 3 Geo-referencing ............................................................................................................................... 9 Figure 11 Error Massage that will appear when user loads un-georeferenced data in ArcGIS ................................. 9 Figure 12 Step 3 Georeferencing ............................................................................................................................... 10 Figure 13 Step 4 Georeferencing .............................................................................................................................. 10

Figure 14 Step 5 Georeferencing .............................................................................................................................. 11 Figure 15 Step 6 Georeferencing ............................................................................................................................... 12

Figure 16 Step 7 Georeferencing ............................................................................................................................... 12

Figure 17 Step 8 Georeferencing .............................................................................................................................. 13 Figure 18 Step 8 Georeferencing .............................................................................................................................. 13 Figure 19 Checking the accuracy of georeferenced images ..................................................................................... 14

Figure 20 Digitized Map of CST .............................................................................................................................. 15 Figure 21 Satellite image of CST (Source: Google Earth) ....................................................................................... 15

Figure 22 Step 1 Digitization ................................................................................................................................... 16 Figure 23 Step 2 Digitization .................................................................................................................................... 17 Figure 24 Step 3 Digitization ................................................................................................................................... 17

Figure 25 Step 4 Digitization ................................................................................................................................... 18

Figure 26 Step 5 Digitization ................................................................................................................................... 18

Figure 27 Digitized CST map.................................................................................................................................. 19 Figure 28 Aster DEM of Bhutan ............................................................................................................................... 20

Figure 29 3D sketch of DEM .................................................................................................................................... 20 Figure 30 Pixel Value (Elevation) ............................................................................................................................ 21 Figure 31 Flow chart to delineate catchment area ..................................................................................................... 22

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Geographical Coordinate System

1. Geographical Coordinate System

Every point on a graph paper can be represented by X-

coordinate and Y-coordinate. Similarly, every point on earth

surface can be represented by latitudes and longitudes.

Latitudes are the imaginary lines on 3D surface of Earth that

run from east-west direction. Longitudes are the imaginary

lines that are drawn on the 3D surface of earth running from

North Pole to South Pole. The surface of earth can be

represented by the crisscrossing network of latitude and

longitude.

A geographic coordinate system is a method for describing

the position of a geographic location on the earth's surface

using spherical measures of latitude and longitude. These are

measures of the angles (in degrees) from the center of the

earth to a point on the earth's surface when the earth is

modeled as a sphere. (ArcMap Help). Yellow lines are the

latitudes and white lines are longitudes

2. Maps and Projections

Map projection is the systematic transformation of 3D earth

surface to 2D plane sheet of paper. While doing such

transforming some of the properties of the spherical earth such

as (a) area (b) shape (c) distance and (d) directions are distorted

or sometime lost. Transformation in general are the sets of

mathematics algorithm than converts’ 3D earth surface into 2D

plane with much less distortions. There exist several projections

system namely, Mercator projection, cylindrical projection,

conical projection planar or Azimuthal projection.

Figure 1 The Earth

(source: Google Earth)

Figure 2 The Schematic representation of Map Projection

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Introduction to GIS

Geographic Information System GIS is a computer-based system that

provides the following four sets of capacities to handle georeferenced

data

Data capture and preparation

Data Management, including storage and maintenance

Data manipulation and analysis

Data presentation (Huisman & DeBy)

GIS is a computer-assisted system for the acquisition, storage,

analysis and display of geographic data. GIS can display a stacked

set of map layers.

Typically, each layer will contain a unique geographic theme or data

type. These themes may include, for example, topography, soils,

land-use, or infrastructure such as roads, pipelines, or sewer

networks.

GIS stores information about the world as a collection of thematic

layers that can be linked together by geography.

Figure 3 Schematic representation of GIS

Figure 4 Thematic layers in GIS

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3. GIS Data model

Spatial Data – Describes the absolute and relative locations of geographic features

Raster data - grid-cell data structure where the geographic area is divided into cells identified

by row and column

Vector data – all the features on the earth can be represented by line (road, river..etc) point

(trees, electrics poles..etc) and polygon (country boundry, lake building…etc)

Attribute data – describes characteristics of the spatial features. These characteristics can be

quantitative or qualitative. Attributes are often referred to as tabular data

Figure 6 GIS data model

Figure 5 Vectors Icon (in ArcGIS)

Lines Polygons

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4. Geo-Referencing

The process of assigning coordinates to a scanned map/ areal images or any dataset to be used in GIS is called

Geo-referencing. GIS can only process geo-referenced data. If user tries to use data without georeferenced in

GIS, it gives a warning message saying “Missing Spatial Reference”.

4.1 Exercise On Geo-Referencing using ESRI ArcGIS Desktop

After opening ArcMap first step is to assign coordinate system to the layer. On the left hand side panel there

is an icon named Layers, right click on it and go to its properties.

Figure 7 Step 1 Geo-Referencing

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Click on "Coordinate System" tab. Many coordinate options are available. For this exercise navigate to predefined - Geographical Coordinate Systems - world - WGS 1984. After selecting WGS 1984 coordinate system click OK.

In ArcGIS it is only possible to handle Geo-Referenced data. Data can be google earth image/ satellite image or any

scanned map. One can manipulate a map that is in hardcopy by loading its scan copy into ArcMap. The scanned

document may be in different file format such as .JPEG, .PNG etc.. However, these data lack spatial reference,

therefore the first step is to assign coordinates to the map. For example, the following map is the scan copy. To

manipulate it in ArcMap, first it needs to be geo-referenced.

Figure 8 Step 2 Geo-referencing

Figure 9 Map of Bhutan

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Instructions to Geo-Reference a map/image in ArcGIS

Step 3: Load the file into ArcMap.

After opening a new ArcMap and assigning coordinate system to layers, add data into ArcMap

Navigate to the folder where data is located in your computer and add the file. As you add the file "Unknown Spatial

Reference" Error message will pop out. It indicates that the file you loaded does not have coordinates assigined.

Click OK.

Figure 10 Step 3 Geo-referencing

Figure 11 Error Massage that will appear when user loads un-georeferenced data

in ArcGIS

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Step 4 Enable Geo-Referencing Tool bar and start Geo-referencing.

If this screen does not appear than right click on loaded

file and "Zoom to Layer"

Figure 12 Step 3 Georeferencing

Right click on gray portion on top of ArcMap

and enable Georeferencing tools


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Step 5 Go to geo-referencing and dis-able Auto Adjust.

Step 6 Add Control Points

Place the cursor on the point where both the coordinates are known. Then left click on that point to mark. Again

right click on the same point to input the x and y coordinates.


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Step 7:

After assigning coordinates to at least four points, enable Auto Adjust. The image automatically adjusts itself to

rectify errors, if there were any. To do so click on link table icon and enable Auto Adjust.

Residual must not exceed 0.05 at any

cases. If it exceeds than repeat the

procedure.

. . .


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Final step: Save the Geo-Referenced Map

Then the image must be rectified and saved to desired folder.

Finally fill up the template box that appears on the screen when rectify is enabled.



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To see whether the new file is properly geo-referenced or not, open Arc-Globe and add the new file. The new file

must exactly overlap Bhutan on the Globe.

If the geo-referenced image exactly overlaps Bhutan in the ArcGlobe it can be concluded that the coordinates

assigned were correct.

Figure 19 Checking the accuracy of georeferenced images

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5. Digitally Representing Geographical data

Figure 21 Satellite image of CST (Source: Google Earth)

Figure 20 Digitized Map of CST

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Figure 21 is the Google Earth image of CST campus and figure 22 is the digital representation of CST campus.

The process to represent geographical data digitally is called Digitization or vectorization.

Almost all the geographical data can be classified into three features class namely point feature class, line feature

class and polygon feature class. These feature classes in ArcGIS terminology is called Shapefile.

For example:

Table 1 Use of Feature class (shape file) that can represent Geographical features

5.1 Exercise on Digitization

Step 1. Load the

georeferenced

image on

ArcMap.

Geographical Features Feature class(shape file) that can represent

Geographical features

Road, River, Stream, electric lines Poly-line

Building, Water Bodies, Forest Polygon

District Head Quarter, Trees, Bus Stop, Point

Tashichoedzong, statue of liberty, Point

Through Arc Catalog navigate to the desired folder where

the new generated files (shape files) are to be saved.

Figure 22 Step 1 Digitization

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On the right hand side panel, right click on the desired folder. Go to New and select shape file.

Next, give an appropriate name, specify the type of shape-file and specify its coordinate system.

Specifying the coordinate system is very important. The coordinate system of the georeferenced file (parent file,

from which features are to be digitized) and coordinate system of the shape file should never miss match. Therefore,

coordinate system for the new shape file must be imported from the parent file.



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The new shape file will automatically be loaded into ArcMap. Next, enable Editor tool bar. (if it is not available

on the top row, right chick on the gray portion and enable Editor tool bar). After that Start Editing.

As "Start Editing" is clicked, a new window titled "Create Feature" will pop up. Select the shape file, take an

appropriate construction tool and start digitizing the feature.

If the "Create Feature" template does not show up, click on an icon as shown in the following figure. (it is located

on Editor Tool bar)



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Once vectorization/ digitization is completed, go to "Editor" and save edits. Similarly, all the features can be

digitized.

Figure 27 Digitized CST map

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Figure 28 Aster DEM of Bhutan

6. Raster Data Processing (Digital Elevation Model Processing)

Digital elevation model (DEM) is a terrain model. It basically has elevation data stored in it. 3D view of DEM of

Bhutan is shown above. For ease to interpret, pixel with same elevation are in same color. In the above case, low

elevations are in purple whereas high elevations are in dull green. Elevation information are stored by each pixel and

such data where pixels stores the information is known as raster data. Size of pixel determines the quality of data.

Smaller the size of pixel better the quality of data.

The square boxes are the pixel and it holds elevation information. Slope, Aspect, Contour are other parameters that

depend on elevation. Since DEM holds elevation data, all these parameters can be generated form DEM.

Navigate to;

Arc tool box Spatial Analyst surface

Figure 29 3D sketch of DEM

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Figure 30 Pixel Value (Elevation)

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Figure 31 Flow chart to delineate catchment area

7. Delineating watersheds

While carrying out a study involving hydrology and projects inclined toward water resource or agriculture, it

becomes necessary to carry out investigation on catchment area. The main purpose of watershed delineation is to

define the boundaries of the catchment area and to divide the area into discrete land and channel segments to analyze

watershed behavior. Delineation of watershed depends on the catchment drainage pattern of the watershed and this

in turn depends on the relief of the area considered. Before delineating, area of interest must be extracted from the

whole DEM.

To extract area of interest, firstly draw a polygon covering the entire study area. Use spatial analyst tool

"Extraction by mask " to extract only the interested area. There after use the Hydrology tools available on

Spatial Analyst in Arc tool box to generate water basin.

SECTION 2 GIS for Engineers

ABSTRACT Participants will be working with ArcMap,

an application within ArcGIS Desktop, to

visualize and analyze geographical data,

create maps, question and retrieve

information through several exercises.

Kirtan Adhikari College of Science and Technology [email protected]

Section 2 is not as elaborative as section 1, during the time of confusion participants are expected to self-explore

by seeking help from ArcGIS Desktop Help (press F1 to open ArcGIS Desktop Help).

It would be ideal to advance into this section only if participants are well versed with the general terms used in GIS

and confident to complete the exercises of section 1 without support. It is recommended to practice the exercises of

preceding section couple of times before moving on into this portion.

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Contents

1. Exercise on Attribute Data (Tabular Data) ------------------------------------------------------------------------------- 2

1.1 Analysis of data on Attribute table ------------------------------------------------------------------------------------ 3

1.2 Next, select all Dzongkhags with area less than 3000 km2 ------------------------------------------------------ 4

1.3 Exercise on Importing tabular data from other software (Excel) ----------------------------------------------- 6

2. Exercise on Data Presentation ---------------------------------------------------------------------------------------------- 9

3. Exercise on Producing a Map (Layout) --------------------------------------------------------------------------------- 12

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1. Exercise on Attribute Data (Tabular Data)

Navigate to the folder where you have saved the data and load the Dzongkhag data (located inside BTN_data

folder). Open its attribute table by right clicking on the Dzongkhag located on table of content (TOC). Take note

of the following:

1. Attribute table is a table consisting of row and column just like excel sheet. It is possible to add more

column as per the requirement. It is also possible to perform mathematical operation in each cell just like in

excel sheet. The columns are also called as fields.

After the Dzongkhag shapefile is loaded, the screen will appear as shown in the figure below without labels. Right

click on the Dzongkhag on TOC and select Label Features. Observe that when a row on attribute table is selected

it simultaneously selects the polygon on the screen.

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1.1 Analysis of data on Attribute table

As indicated earlier, fields (column) can be added or deleted. Let’s add a field named Area.

After clicking on Add Field the second template appears where additional information of the new field created has

to be filled. The data type of Area is number so select Float. Following Table will help you to select the data

Type.

Source: ArcGIS Desktop Help

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Our interest is to compute area of each dzongkhag so select Area field and click on Calculate Geometry.

(Caution: to compute the properties such as area, perimeter, it is recommended to use projected

dataset.)

1.2 Next, select all Dzongkhags with area less than 3000 km2

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click on Select By Attribute…, the template shown like in the figure below will appear, write the simple coding and

get the result.

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1.3 Exercise on Importing tabular data from other software (Excel)

It is a common practice to record tabular data in excel spreadsheet and many a time there arises an incident where

we want to use excel data on ArcGIS. In the following exercise we will try bringing excel data on ArcGIS plat

form. Male population, female population of each dzongkhag is recorded in excel sheet which we want in ArcGIS.

To transfer these data to ArcGIS there must be at least one field common in both the tables (Excel and attribute

table). Note that common field is DzgName. The orientation of data on the field does not matter but the content

must be common. (same on both the fields). ArcGIS compares each data on the common field and transfer data

from excel to matching data in GIS.

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Right click on Dzongkhag Joins and Relates Join.

After selecting Join a new window will appear (refer figure in next page). Provide the necessary information and

click OK.

1. Choose the field in this layer that the Join will be based on.

From the drop down list select the field which is common on both the tables.

2. Choose the table to join to this layer, or load the table from disk.

Navigate to the location where the excel workbook is kept and select.

3. Choose the field in table to base the Join on.

The excel can have multiple fields, select the common field.

There can be many fields in external source (excel) it’s up to the user to decide whether to transfer all the records

from excel or just the matching ones.

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2. Exercise on Data Presentation

ArcGIS provides verities of options to present data on map. User can decide the best option to present data on the

map. Word Symbology is associated with symbolizing or representation of data using various means.

To navigate to Symbology: Right click on the layer, Properties Symbology

Depending on data type a suitable representation scheme can be selected. In this exercise, we want to give

different colour to each dzongkhag polygon. Categories Unique values Add All Values. This action will

result into the map shown in next page. There are many other options such as colour scheme to choose from.

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Similarly, if the data type is numerical values that you want to represent on map. Symbology Quantities select

the field (in this case area) select the colour and click OK. Instead, if you want to present in the form of a chart,

it can be done by navigating to Symbology Charts select the field (in this case area) select the colour.

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Similarly different representation ways can be selected. Symbology Quantities Graduated Symbol select

the field (in this case area) Template

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3. Exercise on Producing a Map (Layout)

In any GIS related project, the final output is always a Map. In this section we will explore ArcGIS Layout View.

When the ArcMap is opened for the first time, the blank screen appears. On this screen we visualize any layer that

is loaded in ArcMap. This screen is known as Data View in ArcGIS terminology. There exists another view where

we can work to produce Maps. This view is known as Layout View. Navigate to View Tab to select Layout View.

You can switch between the views depending upon the task you are performing. If we are interested in analysis,

we work in Data View and if we want to produce maps than we work on Layout View.

Layout view screen looks similar to the image below.

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Enable the Layout toolbar. Right click anywhere on the grey portion and select Layout. Hover mouse over each

icon to understand functions of each icon present on the tool box.

When we are interested to produce map, we have to decide few things before proceeding further;

1. Size of the map.

For this exercise we will work on A4 size. We want to produce maps we created in preceding exercises.

Click on Change layout tool. Next, user have to select a template. Select ISO (A) A4 landscape

template. You can select any template based on your requirement.

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Load Data, and the screen appears like the image below.

Notice that the map is not covering whole paper space. Right click on the blue dotted line perform the action as

indicated in the following figure.

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Double click on the map to select and use pan and zoom tools to orient your Map on the page. It is a good practice

to give more emphasis to the map compared to map elements (Legends, North arrow, scale). Once you have

oriented the map in position, insert Map elements.

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There are many map elements available however it is advised not to use all, instead put most appropriate ones.

Most common Map elements are,

1. Legend

2. North Arrow

3. Scale

4. Title

5. Author, coordinate system, date, logo, etc are optional.

After the map is ready, export the Map in desire file format. It can be exported as PDF, JPEG, PNG etc.

Navigate to File tab Export Map select file format, output location, and click OK. Out put is shown below.

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Similarly it is possible to generate maps of study area while doing research .......................


Mini Project on

Suitability

Analysis


Note

College of Natural Resources(CNR), Royal University of Bhutan and the Interfaculty

Department of Geoinformatics - Z_GIS, University of Salzburg, Austria had jointly organized a

faculty development workshop and dissemination seminar on Geospatial Methodology to Assess

Climate Change Adaptation Strategies for Traditional Economy in Bhutan from 30th March to

1st April, 2015 at CNR Lobeysa. The event was co-funded by The Commission for Development

Research (KEF), Austria. I along with few other CST faculty and student attended workshop and

this document was prepared as an output to share the knowledge gained on Geographical

Information Science and Geographical Information System with other CST staff and students

who could not attend the workshop.

Content

1) Methodology Development

2) Literature Review

3) Tutorial on Suitability Analysis

Acknowledgement

First of all, my heartiest acknowledgment goes to the coordinators Dr. Shahnawaz and Mr.

Ugyen Thinley for their guidance, inspiration and unwavering support rendered throughout the course

of workshop.

I would like to acknowledge the management of College of Science and Technology for

providing the opportunity to me to attend the workshop entitled Geo M4-CCAS. I also would

like to acknowledge Mr. Tshering, Dean Research, College of Science and Technology for

providing continued support during the course of workshop.

Immense gratitude to College of Natural Resources, Royal University of Bhutan for providing

various facilities in lab and necessary equipment required during the course of the workshop.

Lastly I would like to thank all those who have contributed directly or indirectly through the course of the

workshop. Thank you all.


Methodology Development

The main objective of this exercise is to find suitable area for paddy cultivation. We need three

data (DEM, Climate data, Land Use Land Cover) in digital form to find suitable area within

Bhutan for paddy cultivation. The analysis is carried out in ESRI ArcGIS Desktop and the

process is known as suitability analysis.


Literature Review

Factor that affects the paddy cultivations are:

1. Topography

In Bhutan where mountains are predominant feature, terraces have been carved on the steep

slopes where paddy crop depends on favorable weather conditions. Topography can be

classified into following 4 categories depending upon the land slope:

a. 0-15 degree- Highly Suitable

b. 15-30 degrees - Moderately Suitable

c. 30-45 degrees - Less Suitable

d. 45-60 degrees - Least Suitable

2. Altitude

Paddy crop grows very well in humid and relatively flat land compared to sloppy land with

cold climate. In mountainous area such as in Bhutan altitude plays a vital role in

determining climatic conditions of a place. The climatic condition of a place is dominated

by its altitude. Altitude is also categorized in 4 different zones as follows:

a. Wet Sub Tropical < 600 m Highly Suitable

b. Humid Sub Tropical 600 m -1200 m Moderately Suitable

c. Dry Sub Tropical 1200 m -1800 m Less Suitable

d. Warm Temperate 1800 m - 2600 m Least Suitable


3. Climate (Temperature and Rain fall)

Paddy crop requires hot weather and humid place as it cannot grow well without a plenty of

water. For this exercise we are not using the temperature data as it was not available.

However, to carry out suitably analysis it is important to consider all the factors to get

accurate result.

We know that altitude is the key factor that affects temperature and rainfall in mountainous

area. If altitude of a place is known climatic conditions of that place can be assumed and

vice versa.

For this exercise we are using this indirect method to classify the topography into 4

different climatic zones.

Altitude Temperature Rainfall

Sub -Tropical < 600 m Max 35, Min 12, Mean 24 2500 mm - 5500 mm

Humid - Tropical 600 m - 1200 m Max 333, Min 3, Mean 20 1200 mm - 1500 mm

Dry - Tropical 1200 m - 2600 m Max 29, Min 12, Mean 24 Less than 1200 mm

Sub -Tropical Highly Suitable

Humid - Tropical Moderately Suitable

Dry - Tropical Less Suitable


Tutorial on Suitability Analysis

Inside your working folder create three additional folders

1. Work

2. Data

3. Result

I have created a folder named Suitability Analysis in drive D, inside which I have created 3 more

folders and have stored the data in data folder. While working with ArcGIS, naming folder and

folder destination must be done cautiously.

Open ArcGIS and load Aster dem (AsterDEM_Version3_drukref03.img) which is in data folder

inside DEM folder.


As you can see that it is a digital elevation model and our interest is to find suitable land for

paddy cultivation. Now extract only Bhutan from the AsterDEM_Version3_drukref03.img

To do so, load the Bhutan boundary shape file (it is inside National_data) and extract by mask.

Store your dem_btn (new extracted file) in work folder.


Now your screen will be as shown above. To extract only region within Bhutan open tool box

spatial analyst tools Extraction Extraction by Mask. Give appropriate file name (dem_btn)

and store it in work folder.


Remove other layers and keep only dem_btn

We now have to reclassify this dem as per our requirements. We have seen that paddy cultivation

can be affected by slope of the land so we classify the slope. Before that, we have to create slop

Map. Go to 3D analyst tools Raster surface slope.

New file is named slope_btn and store it in work folder.


Next step is to reclassify the slope_btn into 4 catogory. 3D Analyst Raster Reclass

Reclassify.

Click on Classify

Select Method as Manual, Classes 4, and break

values as 15, 30, 45 and 60


Enable Change missing values to NoData and save the output in work folder and Name it as

re_slope


Altitude Reclassify

After reclassification of dem your screen will be similar to the image below.


Rainfall Interpolation

Rainfall is measured by installing rain measuring gauges at various points. The drawback of such

record is that it is a point data and rainfall is an even that covers large area at an instant. The data

we have is point data, now our task is to interpolate the data so as to get rainfall over entire

Bhutan.

Load the rainfall data into ArcGIS.

After you load the rainfall data on ArcGIS, right click and click on "Display XY Data" and again

click ok on the window that appears.

Now your screen will appear this way


Whatever appeared on the screen is just temporary, so now we need to export the rainfall data as

Shape file format (.Shp) so that we can manipulate.


Select out-put dictionary to work folder and file type as shape file (.Shp). In this case new shape

file is named as rain. Right click on rain and view its attribute table.

The data which was in excel file is now brought into ArcGIS as a shape file.


To interpolate rainfall Kriging method is employed. Spatial Analyst tools > Interpolation >

Kriging.

In this case points are less and the extent to be interpolated is large; if you interpolate simply, the

result will not cover entire Bhutan therefore we have to play a simple trick here.

One trick around is to put some fake points around the perimeter of the region of interest. Place

them beyond the intended extent of the extrapolated values by a distance greater than the

maximum neighborhood search radius. This will prevent the fake data from affecting the results

but ought to persuade the software to perform the calculations you desire.

Notice the fake points have been created around Bhutan which was not there in the beginning.

Next reclassify rain fall data. To interpolate rainfall, mean rain in the month of July was used.

Reclassifying is done in this fashion.

a. 5 mm - 15 mm Least Suitable

b. 15 mm - 30 mm Less suitable

c. 30 mm - 45 mm Moderately Suitable

d. < 45 - Highly Suitable


Weighted Overlay Analysis

Overlay analysis is a group of methodologies applied in optimal site selection or suitability

modeling. It is a technique for applying a common scale of values to diverse and dissimilar

inputs to create an integrated analysis.

Suitability models identify the best or most preferred locations for a specific phenomenon. Types

of problems addressed by suitability analysis include:

Where to site a new housing development

Which sites are better for deer habitat

Where economic growth is most likely to occur

Where the locations are that are most susceptible to mud slides

Overlay analysis often requires the analysis of many different factors. For instance, choosing the

site for a new housing development means assessing such things as land cost, proximity to

existing services, slope, and flood frequency. This information exists in different raster with

different value scales: dollars, distances, degrees, and so on. You cannot add a raster of land cost

(dollars) to a raster of distance to utilities (meters) and obtain a meaningful result.

Additionally, the factors in your analysis may not be equally important. It may be that the cost of

land is more important in choosing a site than the distance to utility lines. How much more

important is for you to decide.


Even within a single raster, you must prioritize values. Some values in a particular raster may be

ideal for your purposes (for example, slopes of 0 to 5 degrees), while others may be good, others

bad, and still others unacceptable.

The following lists the general steps to perform overlay analysis:

1. Define the problem.

2. Break the problem into sub-models.

3. Determine significant layers.

4. Reclassify or transform the data within a layer.

5. Weight the input layers.

6. Add or combine the layers.

7. Analyze.

Steps 1–3 are common steps for nearly all spatial problem solving and are particularly important

in overlay analysis.

(Source: ArcGIS Desktop Help)


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Arc gis tutorial and gis traning manual

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