(1) (iii) Measurement
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Transcript (1) (iii) Measurement
Geographic Information Systems
GIS Analysis and Modeling
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
2. 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 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) Conflation
The procedure of reconciling the positions of
corresponding features in different data layers (e.g.
snapping).
4. 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
Attribute 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
Measurements
Retrieval
Classification
Measurements
5. (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) 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)
Classification
Raw data
Classified data
http://www.geog.leeds.ac.uk/courses/level2/geog2750/geog2750_15.ppt
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) Measurement
Distances between Points
- Euclidian distance
5. (1) (iii) Measurement
Nearest distances
The Closest Facility
5. (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
Lengths of lines
Perimeters and areas of polygons
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
Area of a profile
Volume
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
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) Overlay
Arithmetic overlay
Logic overlay
Weighting input layers
Raster vs. vector overlay
5. (2)(i) Arithmetic Overlay
adding layers, subtracting, multiplication, division, etc.
Raster
Input data layer A
Input data layer B
Output data layer
(2)(i) Arithmetic
Overlay
Arithmetic5.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
5. (2)(ii) Logic Overlay
Finding areas where certain conditions occur
Boolean logic
Mary Ruvane, UNC –Chapel Hill
5. (2)(iii) Weighting Input Layers
Professional experiences
Expert votes
Empirical or analytical models
5. (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 Overlay
Vector Overlay
http://www.geoict.net/tgipage/Teaching/UNIT%207--PPT.pdf
Readings
Chapter 5,6,9,10