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