Polygonarea element

1
Polygon/area element

• Chain/ring defines exterior
• area definition may or may not include boundary
• boundary excluded interior area
• boundary included polygon
• actually two components
• interior area
• boundary chain/ring

2
Size of elements

• Generally point elements imply no dimensions
• line elements have implied width
• chains that are area boundaries have no width

3
Dyad

• Important compound object
• combination of two places
• essential aspect is relationship
• relationship can be geographic
• direction, distance
• or conceptual
• migration sources/destinations etc.

4
Net or graph

• special case
• multiple relationships
• paths can be defined
• directionality of links
• directionality relates to movement not digitizing

5
Tessellations

• Term is used in a number of settings but formally
  implies a full partitioning of an area into areal
  units

6
Lattice

• distribution of points
• can be regular
• can be irregular

7
Duals

• substution of one type of unit for another
• examples
• centroid for area of a polygon
• zipcodes areas for inclusive points (addresses)
• vorroni polygons

8
Entities versus fields

• basic issue is that entity is homogeneous
  internally and heterogeneous externally

not-It-ness
It-ness
9
Consideration of variation over space

• most is in fact continuous
• most is represented as discrete
• sample points
• isolines (contours)
• piecewise models
• soils units, census tracts
• define areas unit on some basis of perceived or
  actual homogeneity

10
Phenomena that are discretable

• condition is not present everywhere - lake not
  lake
• condition has significant steps in values it
  has - high crime rate
• multiple conditions do tend to co-occur - soil
  texture/pH/depth to bedrock

11
Continuous phenomena have tropisity

• isotropic - values do not vary with respect to
  direction
• distance from point x
• travel costs increase linearly w/ distance
• anisotropic - values vary with respect to
  direction

12
Spatial and non-spatial properties

• use of data can be both spatial and non-spatial
• non-spatial
• analysis of poverty levels
• spatial
• distance between mediacl providers
• both
• number of low income families associated with
  each medical center

13
Analysis (1)

• attributes of a single class (point, line or
  polygon)
• tracts with more than 50 low income
• tracts with more than 50 low income near tracts
  with 80 high income

14
Analysis (2)

• attributes of pairs of places
• ranking of timber sales numbers between countries
• ranking of timber sales numbers of divided by the
  transportation distance

15
Analysis (3)

• attributes of more than one entity class
• average rain fall for each state
• projected rainfall in beaver watershed

16
Analysis (4)

• analysis which creates new entity class
• buffer zones around a school