Analysis Based on Distance

Analysis Based on Distance

 The ability to calculate and manipulate distances underlies many forms of spatial

analysis

o based on the concept that the separation of features or events on the Earth‘s

surface can tell us something useful

Measuring Distance and Length

 A metric is a rule for the determination of distance between points in a space.

 Pythagorean or straight-line metric is explained with an equation and diagram

o Notes this metric does not work for latitude and longitude, must use the spherical

metric provided in Section 5.7 to calculate great circles

 Distance along a route represented by a polyline is often calculated by summing the

lengths of each segment of the polyline

 Because there is a general tendency for polylines to short-cut corners, the length of a

polyline tends to be shorter than the length of the object it represents.

 Length of a 3 dimensional line measured off its planimetric representation will also be

shorter than its true length

Buffering

 Builds a new object or objects by identifying all areas that are within a certain specified

distance of the original objects

 In raster, buffers can be spread outwards from objects to create friction surfaces

Cluster Detection

 Points patterns can be identified as clustered, dispersed, or random

 Kinds of processes responsible for point patterns are:

o First-order processes involve points being located independently

o Second-order processes involve interaction between points

 Briefly introduces the K function as an example of a descriptive statistic of pattern, and

explains a simple example

source: gis training module book