Spatial relationships

1
Spatial relationships

• J426 Class 18
• March 12, 2009

2
Overview

• Selecting features by location
• Selecting points
• Selecting lines
• Selecting polygons

3
Selection in ArcGIS

• Geographic features linked to records in
  attribute table
• So selection of geographic features also selects
  records in attribute table, and vice versa

4
Selected features on map and in attribute table
5
Forms of selection in ArcGIS

• Selection by attribute
• Selection by location
• Selection by pointing and clicking on feature in
  map or row in table

6
Selecting features by location

• Features can be selected based upon spatial
  relationship to other features
• Can select features that (for example)
• Are contained by
• Intersect
• Are within distance of

7
Select by location

• Select features in specified theme based on
  spatial relationship to (possibly selected)
  features in some other theme
• Types of spatial relationships depend upon types
  of themes

8
Selecting points

• Based on relationship to other points
• Selecting points that are within distance of
  other points
• Selecting points that intersect other points also
  possible
• Based on relationship to line features
• Selecting points that are within distance of line
  features
• Selecting points that intersect line features

9
Selecting points (contd)

• Based on relationship to polygon features
• Selecting points that are completely within
  polygon features (would be same as intersect)
• Selecting points that are within distance of
  polygon features

10
Crimes selected 500 feet from Meridian Street
11
Crimes selected within selected beat
12
Selecting lines

• Based on relationship to point features
• Selecting lines that are within distance of point
  features
• Selecting lines that intersect point features
• Based on relationship to other line features
• Selecting lines that intersect other line
  features
• Selecting lines that are within distance of other
  line features

13
Selecting lines (contd)

• Based on relationship to polygon features
• Selecting lines are contained by polygon features
• Selecting lines that have their center in polygon
  features
• Selecting lines that intersect polygon features
• Selecting lines that are within distance of
  polygon features

14
Street segments selected within selected seat
15
Selecting polygons

• Based on relationship to point features
• Selecting polygon features that contain or
  intersect point features
• Selecting polygon features that are within
  distance of point features

16
Selecting polygons (contd)

• Based on relationship to line features
• Selecting polygon features that completely
  contain line features
• Selecting polygon features that intersect line
  features
• Selecting polygon features that are within
  distance of line features

17
Selecting polygons (contd)

• Based on relationship to other polygon features
• Selecting polygon features that are completely
  within other polygon features
• Selecting polygon features that completely
  contain other polygon features
• Selecting polygon features that have their center
  in other polygon features
• Selecting polygon features that intersect other
  polygon features

18
Beats selected intersecting Meridian Street
19
Beats selected containing homicides
20
Census Blocks Selected within Selected Beat
21
Multiple selections and logical relationships

• Feature selections provide for logical
  combination of queries
• Can add selected features to those already
  selected, meaning current criterion must be true
  or prior selection criteria true
• Can select from features already selected,
  meaning current criterion must be true and prior
  selection criteria true
• Can select out features from those already
  selected, meaning current criterion be not true
  and prior selection criteria true

22
Why select features?

• To control which features are displayed
• To obtain statistics for some attribute on
  selected features
• Most importantly, as one step in larger analysis
• For example, in obtaining total number of
  robberies for beats, would need to select
  robberies from all other crimes