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. Overlay Arithmetic overlay Logic overlay Weighting input layers
Raster vs. vector overlay

5. 3.1 Arithmetic Overlay
adding layers, subtracting, multiplication, division, etc.
Raster
Input data layer A
Input data layer B
Output data layer

6. 3.1 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

7. 3.3 Weighting Input Layers
Professional experiences
Expert votes
Empirical or analytical models

8. 3.4 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

9. Raster Overlay Vector Overlay

10. 3.2 Logic Overlay Finding areas where certain conditions occur
Boolean logic
Mary Ruvane, UNC –Chapel Hill

11. Union INPUT COV UNION COV OUT INPUT COV UNION COV # # ATTRIBUTE # ATT
# ATTRIBUTE # ATTRIBUTE
1 1
2 A
3 B
4 C
5 D
OUT INPUT COV UNION COV
# # ATTRIBUTE # ATT
3 2 A 1
4 2 A
5 3 B
6 3 B 1
7 2 A
8 3 B
9 4 C
10 5 D
11 4 C 1
12 4 C
13 5 D
14 5 D 1
Figure 4.2: Buffers around points, lines and a polygon In all cases the buffer polygons are shaded light grey while the input features are in black.

12. Intersect and Identity

13. Clip

14. Erase

15. Update

16. 4. Proximity Analysis (Buffering)
The identification of a zone of interest around an entity or a set of entities

17. Buffering

18. Buffering A multi-distance buffer (each ring is 150 m)
A single distance buffer (250 m)

19. 5. 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

20. 5. Measurement ..
Distances between Points
- Euclidian distance

21. 5. Measurement ..
Nearest distances
The Closest Facility

22. 5. Measurement .. Functional Distance
Three-minute response time from a fire station, City of Phoenix

23. 5. Measurement ..
Lengths of lines
Perimeters and areas of polygons

24. 5. 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,

25. 5. Measurement ..
Area of a profile
Volume

26. 5. 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

27. 5. Measurement ..
Sinuosity of a line - the ratio of the actual length to the straight line length between point A and point B

28. Readings
Chapter 5,6,9,10