Vector Analysis
Where have we come so far?
• By now, you should be familiar with: – What GIS is – How GIS works – Some of what GIS can do – GIS data formats
• Spatial data • Tabular data
– Modifying display of data
What comes next?
Spatial Analysis
Overview
• Selection • Topological Overlays • Buffering
Selection
• Examples:
– Which census blocks are within 10 km of a superfund site?
– Which ecoregions are projected to experience the greatest changes in climate?
– Which building sites are on parcels with some old growth forest?
Selection
• Examples:
– What is the age-class distribution of stands adjacent to stands younger than 10 years?
– What is the average slope of stands within 50 m of a stream?
– Where are vacant properties close to Interstate 5?
Selection is based on spatial relationships
• Relationships between features – Proximity – Containment – Overlap
• All based on feature geometry
Selection
– Selecting points near a line (proximity) – Selecting adjacent features (proximity) – Selecting lines within polygons (containment) – Selecting polygons that contain lines (overlap) – Selecting points within polygons (containment) – Selecting polygons that contain points (overlap) – Selecting polygons that overlap polygons (overlap)
Selection
Selecting points near a line
Selection
Selecting adjacent polygons in the same layer
Selection
Lines within polygons
Selection
Polygons that contain lines
Selection
Points within polygons
Selection
Polygons that contain points
Selection
Polygons that overlap other polygons
Selection
• Definitions – Target layer:
the layer we want to know something about – Selector layer:
the layer we are spatially referencing to
• Which streams cross stands > 200 ha?
Types of spatial relationships
Topological overlay:
• Combine multiple layers to create new layers
• Different types of overlays
• Quantify length/area of overlap
• All functions are accessed with ArcToolbox tools
Input and overlay layers
• Input layer is the “bottom” layer • Overlay is the “top” layer • For some types of overlays it matters
which of the two layers are on top.
Topological overlay:
• Always uses polygon as the overlay layer • Output is the same as the input
Topological overlay: How it works
• Features from different layers are combined to create a layer with new features
Topological overlay: How it works
• New nodes are created • New lines and polygons are built
Topological overlay: How it works
Alfisol
• Lines are split at polygon boundaries • Lines take on attributes of overlapping polygons
ArcGIS does NOT automatically update geometry fields for
shapefiles
Topological overlay: Types
• Union • Clip • Identity • Intersect • Update • Erase
Union null value =
""
null value =
0
• Combines layers • All features from both
input and overlay layers remain
• Attribute values are assigned by containment
• Attribute inheritance • Polygon & polygon only
Union: Example
Identity
polygon on polygon, line, or point
1
• Input layer takes on “identities” (attributes) of overlay • All features from input layer are retained • Attributes from both layers exist
where there is overlap • Order of input and overlay matters
Identity: Example
input overlay
Intersect
• Only features from area of intersection exist in output • Attributes from both layers exist • Order of input and overlay does not matter • Polygon on polygon, line, or point
Clip
• “Cookie cutter” • Only features and attributes of the input layer are
retained • Polygon on polygon, line, or point
Clipping… an example
Clipping… an example
Buffering
Buffering • Define a constant or variable width from input
features • Creates a whole new data layer
Ecological Applications: Vol. 17, No. 1, pp. 140–153.
A META-BACI APPROACH FOR EVALUATING MANAGEMENT INTERVENTION ON CHRONIC
WASTING DISEASE IN MULE DEER
Mary M. Conner, Michael W. Miller, Michael R. Ebinger, and Kenneth P. Burnham
ArcGIS does NOT automatically update geometry fields for
shapefiles
Dissolve (not really an overlay method)
• Works on a single layer • Removes boundaries between polygons or
nodes between arcs • Features with same attributes are dissolved
Landscape Ecology © Springer Science+Business Media, Inc. 2006 10.1007/s10980-006-9049-3
Research Article
Spatial patterns of Mediterranean land abandonment and related land cover transitions
Raymond Sluiter and Steven M. de Jong
Digital map data Major and minor roads, trails, walking paths, land use, streams and lakes (1:25,000 ) Soil classes were digitised from a 1:100,000 soil map Geological units were digitised from geological maps (1:50,000)
Aerial photographs Black and white aerial photographs from 1946, 1954, 1970, 1971, 1983 and 1988 Colour aerial photographs in 1996 and 2001. Scales were ranging from 1:17,000 to 1:25,000. After scanning and processing of the images the resulting cell size was 1 m to detect small individual trees and detailed vegetation patterns.
Aerial photograph interpretation and change detection
recently abandoned
recently abandoned
older abandoned natural succession
natural succession & older succession
natural to tilled & natural to urban
Homework
• For next week, read “Vector Analysis 2” “Help Topics”
•
• Assignment 5 (due May 2nd)
Ecological Applications: Vol. 16, No. 1, pp. 186–201.
Identifying Potential Indicators Of Conservation Value Using Natural Heritage
Occurrence Data Peter B. Pearman, Michael R. Penskar, Edward H. Schools, and
Helen D. Enander
