INTRODUCTION TO GEOGRAPHICAL INFORMATION

SYSTEM

INTRODUCTION TO GIS

Used to describe computer facilities which are used to handle data referenced to the spatial domain.

Has the ability to inter- relate datasets and to carry out functions to improve their analysis and the presentation of the results.

DEFINITON OF GIS GIS is defined as

“ a set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes.”

A computerized system for capturing, checking, manipulating analyzing and displaying data related to positions on or near the earth’s surface.

EVOLUTION (from mapping to GIS) Topological technique permitted the data not

only to determine where a point or a line or an area was located but also to analyze those features.

GIS data can be assembled by

-existing databases

-digitized or scanned from existing maps

-GPS surveying techniques

DEVELOPMENT WITH MODERN GIS Modern GIS developments are based on a data

theory.

There are several aspects are considered:GIS specific characteristic

a) location-coordinates and street address

b) attributes-features that being analyzed

GIS activities can be by two board field

a) geographic

b) cultural

ADVANTAGES of GIS

Storage and easily update data Sort and store spatial features Allow to zoom into section of data to graphic

and text which may be hidden Analyze both entities and data using

sophisticated computer programs Allow user to prepare maps

Allow user to use data to prepare maps at different scales

Allow to import stored data electronically and save the cost of collecting data

Build and augment a database Create new maps by modeling or reinterpreting

existing data

COMPONENTS OF A GIS It can be divided into 4 major activities:

- Data collection and input.

- Data storage and retrieval.

- Data analysis.

- Data output and display.

GIS FUNCTIONAL ELEMENTSData

Collection and Input

Digital

Data Storage and Managemen

t

Data Retrieval

Data Manipulation and Analysis

Data Display

Image Copy

Hard Copy

GIS TYPICAL COMPONENTS: The computer with GIS software is the main

component and typically uses Microsoft or Unix operating systems.

Data collection can be divided into geometrics components that are:

- Field surveying,

- Remote sensing,

- Digitalization of existing maps and plans,

- Digital data transfer via Internet or CD/DVD

Computer storage:

- Hard disks,

- Optical disks etc. Software designed are to download, edit, sort and

analyze data. It also designed to process and present data in the

form of graphics and maps and/or plans.

SOURCES FOR GIS DATA: The most important part of GIS is the collection of

data. If data can be obtained from other sources, the

efficiency of the process increases.

Traditional sources for data collection:

- Field surveying.

- Remotely sensed images.

- Existing topographic maps, plans etc.

- Electronic transfer of previously digitalized data from Government agencies or commercial firms.

DATA SOURCES

GIS

DATA SOURCE

S:Structur

al, Construction,

Hydrology,

Environmental.

DATA MANIPULATION:Highwa

y design,

Site plannin

g, Landsca

pe plannin

g, Drainag

e analysis

.

DATA CATEGORISATIONNode Arc Polygon

• point Independent arc Independent single polygon

Independent multiple polygon

• point with vertical information

Independent multiple arcs

Contiguous polygon

Point in polygon

• arc junction Connected arcs network

overlap noncontiguous

GIS DATA STRUCTURE

GIS data structure can be divided into

Spatial data

Attribute data

GIS DATA STRUCTURE

Spatial

Vector data

format - positional data is represented

in form of

coordinates

Raster data

format – consists of a set

or matrix of cells or pixels of a specific

size and area.

Attribute

Digital data- record data by using

computer software. Example computer

programming

Non- Digital date – record data by

writing manually.

Example file.

In vector data format, the basic unit of spatial information are points, lines and areas.

Each units is composed as a series of one or more coordinate points.

By using vector systems, there are 3 types of objects possible:NodesArcsPolygons

VECTOR DATA FORMAT

RASTER DATA FORMAT Consists of a set or matrix of cells or pixels of a

specific size and area.

The image represent a scanned map or an aerial

photograph of the site to be modeled.

Point is represented by a single grid cell, a line by

consecutively neighboring cells and an area by a cluster

of neighboring cells.

Can be for merging and investigating the vectorising

method for a specific purpose

Example : raster image with a vector image for movement of river

COMPARISON OF VECTOR AND RASTER

VECTOR DATA RASTER DATA

Represent feature shape more accurately Rectangular representation and more

generalized.

Represent feature with well- defined

boundaries.

Represent a more generalized view.

Compact data structure represented by

simple points, lines and polygons with

topological relationship.

The data structure relatively simple. It uses

rows and column of grid cell having uniform

size.

Resolution of data depends on compilation

method and scale of source data.

The data resolution depends on the cell size.

Easy to represent topological relationships. Difficult to represent topological

relationships.

GEOREFERENCING: Most geographic data users have the same earth-

reference techniques that the data can be shared by using various computer systems.

Coordinate Grids:The plane coordinate grid systems 1983

(SPCS83) has been applied to all states.Software programs readily convert coordinates

based on one projection.

Transformation: If a GIS is tied to a specific coordinate grid and

orientation, the new data needs to be transformed to fit the working model.

Transformations can be made in:

- Grid reference,

- Scale

- Orientation.

The computer programs designed to translate from one grid reference to another, convert the scale, and rotate to appropriate orientation.

DATABASE MANAGEMENT: To organize the data so that the information about

entities and their attributes can be accessed by rapid computerized search and retrieval techniques.

Data collections can range in complexity.

THE END