Lecture 10 : Spatial Analysis of Vector Data (Link to Powerpoint File)

Lab 11 : Vector Data Analysis

Spatial Analysis: 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
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)

Vector Analysis Techniques

Buffering
Overlay
Distance Measurement
Map Manipulation

Vector Buffering

Principle of buffering is to create a buffer zone which contains the area within a given distance of a feature
Can buffer points, line or polygons

Creating buffer zones
Most common technique is a set buffer zone around all features
Can also vary buffer zone distance for features by using a feature attribute to define the size of the buffer zone
Can create multiple buffer zone data sets as well
Note the area size of outer buffers will be larger than the inner buffers

Buffering Applications

Specify that features must be within a specific distance of a feature
Must build within ½ mile of an existing road
Specify that features cannot be within a specific distance of a feature
Cannot drill within ¼ mile of a river
Buffers may be feature classes unto themselves
Road right-of-way

Vector Overlay

Vector overlay techniques are used to combine data from multiple vector layers
Output features contain a combination of attributes from the input vector layers
Vector overlay types
Point in polygon
Line in polygon
Polygon on polygon

Vector Overlay Methods

Two basic overlay methods
Union
Output data set contains all features and data from the input data
Intersection
Output contains only those features spatially overlap

Vector Overlay Issues

Error Propagation
Positional Errors
Mapping inaccuracies of input layers can lead to slivers.
Identification Errors
Errors in input layer attributes will continue through later overlay analyses
Accuracy of composite maps tends to decrease as more input layers are used.
Accuracy of resultant map can never be better than the errors of the most inaccurate source layer.

Vector Distance Measurements

GIS programs contain functions to calculation the distance between features within the same layer or between different layers
Distance measurement methods
Euclidean measurement
Measures the shortest straight line distance between features
Non-Euclidean measurement
Measures distance where euclidean spatial distance is distorted by other factors
Driving distance must be calculated along a road network
Walking distance can take into account the effects of terrain

Map Manipulation Techniques

Map manipulation can be similar to overlay techniques but it does not combine attribute data from the input layers
Dissolve
Combines map features that share a common attribute
Combine spatially adjacent features that share a common attribute
Clip
Limits spatial extent of a layer to be by another input map layer
Merge
Combines spatial discrete input layers to create a map that contains the maximum extent of all the input layers
Differs from edge matching in that the boundaries between the input layers is maintained.