Geographic Information SystemsGeographic Information Systems

GIS Analysis and Modeling

1. Geographic Analysis1. 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

2. Organizing Geographic Data2. Organizing Geographic Data

Data layers (coverage etc.) Feature types: points, lines, polygons

Objects: geometric or thematic

e.g. Development

streets - line layer1

streams - line layer2

parcels - polygon layer1

soils - polygon layer2

3. Maintenance of the Spatial Data3. 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 are registered to a common

coordinate system

Conflation

3.(3) Conflation3.(3) Conflation The procedure of reconciling the positions of

corresponding features in different data layers (e.g. snapping).

4. Maintenance of Attribute Data4. Maintenance of Attribute Data Attribute editing

- List, add, delete, redefine, etc.

Attribute query - Retrieve attributes according to certain criteria

5. Integrated Analysis of Spatial and 5. Integrated Analysis of Spatial and

Attribute DataAttribute Data

The power of GIS lies in its ability to analyze spatial and

attribute data together

Retrieval, classification, and measurements Overlay

5. (1) Retrieval, Classification, and 5. (1) Retrieval, Classification, and

MeasurementsMeasurements

Retrieval Classification Measurements

5. (1) (i) Retrieval5. (1) (i) Retrieval Selective search without modifying the original data (for

output)

http://www.sdsmt.edu/online-courses/geology/mprice/geo416/lecture9.ppt

5. (1) (ii) Classification5. (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)

ClassificationClassification

Raw data Classified data

http://www.geog.leeds.ac.uk/courses/level2/geog2750/geog2750_15.ppt

5. (1) (iii) Measurement 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

5. (1) (iii) Measurement5. (1) (iii) Measurement Distances between Points

- Euclidian distance

5. (1) (iii) Measurement5. (1) (iii) Measurement

The Closest Facility

Nearest distances

5. (1) (iii) Measurement5. (1) (iii) Measurement Functional Distance

Three-minute response time from a fire station, City of Phoenix

http://www.esri.com/mapmuseum/mapbook_gallery/volume17/public2.html

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

5. (1) (iii) Measurement 5. (1) (iii) Measurement

Centroid of an area

Used to represent a polygons by a single point

Several evaluation methods: mean value, center of the enclosing circle or rectangle,

http://www.geoict.net/tgipage/Teaching/UNIT%207--PPT.pdf

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

5. (1) (iii) Measurement 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

5. (1) (iii) Measurement 5. (1) (iii) Measurement Sinuosity of a line

- the ratio of reach length to the straight line distance from point A (bottom of reach) to point (top of reach)

5. (2) Overlay5. (2) Overlay Arithmetic overlay Logic overlay Weighting input layers Raster vs. vector overlay

5. (2)(i) Arithmetic Overlay5. (2)(i) Arithmetic Overlay adding layers, subtracting, multiplication, division, etc. Raster

Input data layer A

Input data layer B

Output data layer

5. (2)(i) Arithmetic Overlay5. (2)(i) Arithmetic Overlay Arithmetic operation on two data layers using the vector data model

Input data layer A

Input data layer B

Output data layer

Spatial data Attribute data

5. (2)(ii) Logic Overlay5. (2)(ii) Logic Overlay Finding areas where certain conditions occur

Boolean logic

Mary Ruvane, UNC –Chapel Hill

5. (2)(iii) Weighting Input Layers5. (2)(iii) Weighting Input Layers Professional experiences Expert votes

Empirical or analytical models

5. (2)(iv) Raster vs. Vector Overlay5. (2)(iv) Raster vs. Vector Overlay Raster

- 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

Raster OverlayRaster Overlay Vector OverlayVector Overlay

http://www.geoict.net/tgipage/Teaching/UNIT%207--PPT.pdf

Readings Readings

Chapter 5,6,9,10