1. An Introduction to Concepts and their Implementation in ArcMap
Spatial Analysis
An Introduction to Concepts
and their
Implementation in ArcMap
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

2. Description and Analysis
Most GIS systems are acquired by large organizations for the purpose of representing and describing features of the real world which are relevant to that organization’s mission
Spatial databases perform this function
Most concepts discussed so far relate to this
Points, lines, polygons concepts for representation
Coordinate systems as fundamental properties of spatial data
geographic file formats for storage
Most GIS system capabilities are focused here
Analysis involves gaining an understanding of the patterns, and associated cause and effect processes, underlying the features which have been described in order to
Help the organization better carry out its mission
Make better decisions, for example
Understand the phenomena as a goal in itself
This is the role of science
GIS systems are less capable here, and often must be supplemented
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

3. Process, Pattern and Analysis
Processes operating in space produce patterns
Spatial Analysis is aimed at:
Identifying and describing the pattern
Identifying and understanding the process
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

4. Spatial Analysis: successive levels of sophistication
Spatial data manipulation: classic GIS capabilities
Spatial queries & measurement, buffering, map layer overlay
Spatial data analysis: descriptive and exploratory
Visualization through data manipulation and mapping
John Snow’s maps of cholera in 1850s London
Spatial statistical analysis: hypothesis testing
Are data “to be expected” or are they “unexpected” relative to some statistical model, usually of a random process
Spatial modeling: prediction
Constructing models (of processes) to predict spatial outcomes (patterns)
What if analyses
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

5. GeoStatistics & Spatial Statistics
Object View
The real world is a series of entities located in space.
An object is a digital representation of an entity
Objects analyzed with Spatial Statistics
The focus of this course
Field View
The real world has properties which vary continuously over space
every place has a value
Fields analyzed with GeoStatistics
The focus of the Spatial Analysis course
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

6. The Pitfalls of Spatial Analysis
Spatial autocorrelation
Data from location near to each other are more likely to be similar than data from location remote from each other
Causes serious problems with traditional statistical models
Spatial statistical models are essential
Modifiable areal unit problem (MAUP)
Results may depend on the areal unit used
Census tracts versus counties (scale issue)
Census tracts versus zip codes (not a scale issue)
Ecological fallacy
Results obtained from aggregated data (e.g. census tracts) cannot be assumed to apply to individual people
A special case of the MAUP problem
Encountered in spatial and non-spatial analysis
Scale affects representation and results
Cities may be points or polygons
MAUP may be viewed as a scale issue
Nonuniformity of Space and Edge Issues
Phenomena is not distributed evenly in space
Bank robberies cluster ‘cos banks are clustered in space
Edges, beyond which there is no data, can significantly effect results
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

7. Fundamental Spatial Concepts
Distance
The magnitude of spatial separation
Euclidean (straight line) distance often only an approximation
Adjacency
Nominal or binary equivalent of distance
Levels of adjacency exist: 1st, 2nd, 3rd nearest neighbor, etc..
Interaction
The strength of the relationship between entities
An inverse function of distance
Neighborhood
An association between one entity and those around it
May be based upon
Interaction: flows or connections (functional)
Similarity of attributes (formal)
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

8. Implementing Spatial Analysis in ArcGIS 9
Primarily carried out in ArcMap:
via Selection/Select by Location
this selects features of one layer(s) which relate in some specified spatial manner to the features in another layer
if desired, selected features may be saved later to a new theme via Data/Export Data
Individual features are not themselves modified
via Spatial Join (right click layer in T of C, select Join/Joins and Relates, then click down arrow in first line of Join Data window---see Joining Data in Help for details)
Use for: points in polygon (identifies polygon in which point is located)
lines in polygon (identifies polygons crossed by line)
points on lines (to calculate distance to nearest line)
points on points (to calculate distance to “nearest neighbor” point)
operate on tables and normally creates a new table with additional variables, but again does not modify spatial features themselves
via ArcToolbox
Generally these tools modify geographic feature, thus they create a new layer (e.g. shape file)
Tools are organized into multiple categories
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

9. GISC 6382 Applied GIS Briggs UT-Dallas
Differences
Selection: simply selects (“highlights”) entire spatial features in the target layer, but doesn’t modify these features
Selection only
Only Selected features (a subset of all features) are “output”
No new output file saved unless you use Export/data
joins: operate on tables and normally creates a new table with additional fields or variables (columns), but again does not modify actual spatial features (rows)
adds attributes (columns) to the layer’s table from another layer’s table
All features are “output”
No features modified
No new output file saved unless you use Export/data
Analysis Toolbox (and others) in ArcToolbox
Often these modify or create spatial features thus they output new spatial files
Different approaches can be used, in some cases, to produce same results.
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

10. Analysis Tools in ArcToolbox
ArcToolbox, particularly the Analysis Tools toolbox contains
Extract toolset, including
Clip which limits one layer to the exact outer boundary of another layer
(e.g. limit a Texas road theme to Dallas county only)
Overlay toolset, including
Intersect, which combines two polygon layers--with output limited to common area
Union, which combines two polygon layers--with output covering full extent of both layers
Proximty toolset, including
Buffer, for creating buffer polygons at a specified distance around points, lines or polygons
Point Distance, for calculating distances between points within a specified radius
Statistics toolset, including
Frequency, which gives you counts of attribute value combinations
Summary Statistics, which gives you summary descriptive statistics for columns in a table, including sum, mean, min, max, etc..
Tools useful for analysis of vector data are located in other toolsets as well!!! For example:
Data Management Tools>Generalization, contains
Dissolve, which removes boundaries between polgyons
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

11. The Components of An Analysis and the elements of its documentation
Objective, which explains the purpose of the analysis and explains why it is significant, possibly including
Hypotheses, which are potential explanations which you intend to test
Literature Review, which identifies the key pieces of existing research relevant to the project and the hypotheses you have advanced
Data Sources, which identify and explain the data used.
Analysis and Methodology, which explains the methodology applied to the data.
Results and Discussion, which describes your main research findings, whether or not your hypotheses were upheld, and any potential problems with your interpretation of the results
Conclusions, which discusses the implications of your finding relative to your initial project objective.
References, which provides standard format citations for all resources drawn upon for the project.
For more detail, go to:
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

12. GISC 6382 Applied GIS Briggs UT-Dallas
Literature Review
All research and analysis builds upon the existing base of scientific knowledge
It is imperative that you identify the existing state of knowledge in order to
Establish appropriate objectives
Advance meaningful hypotheses
Select and use legitimate methodologies
This is accomplished by reviewing the existing literature
On scientific knowledge
On best practices by other organizations
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

13. Doing a Literature Review
Doing a standard Google search is not sufficient! Instead, use Google Scholar
If you access Google Scholar from on-campus via the UTD Library web page at
it will give you automatic access to materials subscribed to by UTD library (very clever!)
For information on how to configure Google Scholar to access UTD library materials from off-campus, go to
This site also gives guidelines on when to use bibliographic databases in place of Google Scholar
Databases available at UTD for literature searches, covering both citations and complete text, can be found at:
The single most commonly used bibliographic database is probably “Web of Science” at
Or directly at
For information on accessing these library databases from off-campus, go to:
Because of licensing restrictions, you will need to follow these instructions for off-campus access
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas

14. How to Format Citations
It is important that you learn to use the correct format when citing literature
Doing a copy/paste of a URL, which may be gone tomorrow, is not sufficient!
The Chicago Manual of Style is the accepted norm.
The Chicago Manual of Style. Chicago: University of Chicago Press, 15th ed., 2003
Or replicate the format used by any mainline GIS journal
A nice summary is available at:
Or,
Use it!!!!
1/3/2008
GISC 6382 Applied GIS Briggs UT-Dallas