Laboratory of Urban and Regional Planning

Department of Architecture – School of Engineering – University of Patras

University of Thessaly, Department of Planning and Regional Development

Databases and Geographic Information SystemsDatabases and Geographic Information Systems

Bases de Bases de DonneesDonnees -- SIGSIG

Vassilis PAPPAS, Associate Professor

vpappas@upatras.gr

Master Franco – Hellenique

“POpulation, DEveloppement, PROspective”

Volos, 2013

Introduction to Spatial Analysis

Spatial Analysis and GIS software

� Spatial analysis is different topic than GIS.

� Spatial analysis is a wide and interdisciplinary scientific topic.

� The aim of a good user is to get immediate and reliable results.

� It is absolutely necessary to know very well the substantial meaning of the

specific variables involved.

� GIS S/W contains some of spatial analysis operators, functions and

techniques and is the main, but not the only, supporting technology.

� Our goal must be to complete our task while investing a minimum amount

of time and effort on learning how to use software.

� The software must give immediate results without requiring from us to

read pages and pages of documentation.

� This task is for our science and not for the software.

Spatial Analysis

A key benefit of GIS is the ability to apply spatial operators to GIS data to

derive new information. This ability forms the foundation for spatial

modelling and geoprocessing.

Working with Spatial Analysis tools it is possible to:

� Derive new information,

� Identify spatial relationships,

� Find suitable locations,

� Calculate travel cost,

� and much more …

Map Algebra

A map layer is a set of spatial entities. As a set, it is possible to apply the

operators of Boolean algebra in order to answer spatial questions.

Intersect, Union and Clip as described in ArcGIS Desktop Help

A spatial question

In an area of 100 meters around the urban public places (green places), in the

city centre, how many buildings, what are they and how much area they cover?

Patras’ central area

Analysis tools

To answer the previous question we are going to perform functions from

ArcGIS Analysis tools (buffer and clip).

Buffer areas

First we choose the layer that contains only green places (as the input layer).

Buffer areas

afterwards we calculate the buffer area of 100 meters and we create a new

layer using the buffer command (proximity).

Buffer areas

then we combine buffer areas with buildings’ layer.

Clip

and we perform the clip command (extract).

Clip

We have create a new layer that contains only the buildings that fulfil the

specific criterion (within 100 meters from green spaces).

Working with attribute table

we calculate the proper variables (“sum” of area and “count”).

Final visualization

we combine the proper layers to have the final mapping synthesis.

The buildings are clipped and they have lost their unique entity as some

buildings are represented with more than one polygon.

Tips on Clip

Selection by location (spatial selection)

We select only the features (with blue perimeter) that are “completely within”

the buffer areas.

Clip Spatial selection

Please study carefully the difference.

Spatial Analysis – Practical exercise

By using the geosets you already have try to reach the following:

� Create a map with population density per

Municipality.

� How many Municipalities and how much is the

average population density across the primary road

network?

� How many settlements are in this corridor?

� Assign the population density per Municipality to the

settlements.