1. Geographic Information Systems
GIS Analysis and Modeling

2. 1. Geographic Analysis Geographic questions: where, when, why, and how
The purpose of the analysis is to answer questions about:
- what existed at where, when, why, and how
- what will happen at where in the future or in other locations

3. 2. Organizing Geographic Data
Data layers (shape file etc.)
Feature types: points, lines, polygons
Object types: geometric or thematic
e.g. Development
streets - line layer1
water - line layer2
parcels - polygon layer1
soils - polygon layer2

4. 3. Maintenance of the Spatial Data
Format transformation
- Spatial data files must be transformed into the data structures and file formats used internally by a GIS software package
Geometric transformation
- Different data layers should be registered to a common coordinate system

5. 4. Maintenance of Attribute Data
Attribute editing
- List, add, delete, redefine, etc.
Attribute query
- Retrieve attributes according to certain criteria

6. 5. Integrated Analysis of Spatial and Attribute Data
The power of GIS lies in its ability to analyze spatial and attribute data together
Retrieval, classification, and measurements
Overlay

7. 5. (1) (i) Retrieval
Selective search without modifying the original data (for output)

8. 5. (1) (ii) Classification
Attribute data
- cerate a new attribute item based on existing ones
Spatial data
-spatial features may be aggregated to larger entities
e.g. Recode in a raster environment
Dissolve in a vector environment
Single layer vs. multiple layers (overlay)

9. Classification Raw data Classified data

10. 5. (1) (iii) Measurement Distances between points Nearest distances
Functional distances
Lengths of lines
Perimeters and areas of polygons
Centroid of an area
Area of a profile
Volume
Shape
Narrowest and broadest distances across a polygon
Sinuosity of a line

11. 5. (1) (iii) Measurement
Distances between Points
- Euclidian distance

12. 5. (1) (iii) Measurement
Nearest distances
The Closest Facility

13. 5. (1) (iii) Measurement Functional Distance
Three-minute response time from a fire station, City of Phoenix

14. 5. (1) (iii) Measurement Lengths of lines
Perimeters and areas of polygons

15. 5. (1) (iii) Measurement Centroid of an area
It is used to represent a polygon by a single point
Several methods to identify a centroid: mean value of vertices’ coordinates, center of the enclosing circle or rectangle,

16. 5. (1) (iii) Measurement
Area of a profile
Volume

17. 5. (1) (iii) Measurement Shape - how to measure shape of an area?
- a compact shape has a small perimeter for a given area
compare perimeter to the perimeter of a circle of the same area - shape = perimeter / area
Narrowest and broadest distances across a polygon

18. 5. (1) (iii) Measurement
Sinuosity of a line - the ratio of the actual length to the straight line length between point A and point B

19. 5. (2) Overlay Arithmetic overlay Logic overlay Weighting input layers
Raster vs. vector overlay

20. 5. (2)(i) Arithmetic Overlay
adding layers, subtracting, multiplication, division, etc.
Raster
Input data layer A
Input data layer B
Output data layer

21. 5. (2)(i) Arithmetic Overlay
Arithmetic operation on two data layers using the vector data model
Attribute data
Spatial data
Input data layer A
Input data layer B
Output data layer

22. 5. (2)(ii) Logic Overlay Finding areas where certain conditions occur
Boolean logic
Mary Ruvane, UNC –Chapel Hill

23. 5. (2)(iii) Weighting Input Layers
Professional experiences
Expert votes
Empirical or analytical models

24. 5. (2)(iv) Raster vs. Vector Overlay
- Every cell is executed, and the overlay result is a new layer
Vector
- The operation is executed only for areas of interest
- New attribute items are created
- New layers may be created that carry both the original and new attributes
- The operation is generally more complex than raster overlay

25. Raster Overlay Vector Overlay

26. Readings
Chapter 5,6,9,10

27. 3.(3) Conflation
The procedure of reconciling the positions of corresponding features in different data layers (e.g. snapping).