Spatial Analysis –
vector data analysis
L2
1/26/2009
Recap: three data models
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Vector
Raster
Geodatabase (object-oriented data model)
• Vector data and table
• feature class is the basis
• Raster data
The real world is complex. Neither discrete (object) nor continuous
(field) can perfectly represent some of real world situations. We need
combined model: dual, hybrid, or object-oriented approach
Spatial Analysis tools in
ArcToolBox
Vector data analysis:
Shapefile &
Feature class/table
Raster data analysis
Details
Vector
Raster
1. Extract
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To create a new subset from the input
(shapefile, features and attributes in a
feature class or table) based on spatial
intersection or an attribute query.
• Clip
• Select
• Split
• Table select
Clip
XY tolerance:
The minimum distance
separating all feature
coordinates (nodes and vertices)
as well as the distance a
coordinate can move in X or Y
(or both). You can set the value
to be higher for data that has
less coordinate accuracy and
lower for datasets with
extremely high accuracy.
Select
Split
Table select
2. Overlay
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Joining two existing sets of features into a
single set of features to identify spatial
relationships between the input features.
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Erase
Identify
Intersect
Spatial Join
Symmetrical difference
Union
Update
3. Proximity
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Identify features that are closest to one
another, calculate the distances around
them, and calculate distances between
them.
• Buffer
• Multiple ring buffer
• Create Thiessen Polygon
• Near
• Point distance
Not dissolved
Dissolved
Example
How to form Thiessen polygons
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Also known as 'Voronoi networks' and
'Delaunay triangulations', Thiessen
polygons were independently discovered in
several fields of study, including climatology
and geography. They are named after a
climatologist who used them to perform a
transformation from point climate stations to
watersheds.
Thiessen polygons can be used to describe
the area of influence of a point in a set of
points. If you take a set of points and
connect each point to its nearest neighbor,
you have what's called a triangulated
irregular network (TIN). If you bisect each
connecting line segment perpendicularly
and create closed polygons with the
perpendicular bisectors, the result will be a
set of Thiessen polygons. The area
contained in each polygon is closer to the
point on which the polygon is based than to
any other point in the dataset.
Statistics
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Basic statistic to the attribute table
• Frequency
• Summary statistics