School of Geography FACULTY OF ENVIRONMENT Point-surface interpolation.

School of GeographyFACULTY OF ENVIRONMENT

Point-surface interpolation

Day 1: point-surface interpolation

• Principles

• Tobler’s First Law of Geography and spatial interpolation

• Classification of methods

• Common methods

• Thiessen polygons

• Trend surfaces

• Inverse distance weighting (IDW)

• TINs

• Geostatistical Analyst in ArcMap

Principles of interpolation

• Tobler’s First Law of Geography

• “Everything is related to everything else, but near things are more related than distant things.”1

• Spatial interpolation

• The procedure of estimating the values of properties at unsampled sites within an area covered by existing observations

• important in addressing problem of data availability

• quick fix for partial data coverage

• interpolation of point data to raster surface

• role of filling in the gaps between observations

1W. R. Tobler, (1970) "A computer movie simulating urban growth in the Detroit region". Economic Geography, 46(2): 234-240.

Classification of methods

• Methods of spatial interpolation:

• many different methods available

• e.g. Thiessen polygons

• e.g. Inverse distance weighting

• classification according to:

• exact or approximate

• deterministic or stochastic

• local or global

• gradual or abrupt

• Remember! Tobler’s First Law of Geography

Common methods

• Thiessen polygons

• Gradual or abrupt?

• Exact or approximate?

• Local or global?

• Deterministic or stochastic?

Common methods

• Trend surfaces

• Gradual or abrupt?

• Exact or approximate?

• Local or global?

• Deterministic or stochastic?

Common methods

Common methods

• Inverse Distance Weighting (IDW)

• Gradual or abrupt?

• Exact or approximate?

• Local or global?

• Deterministic or stochastic?

Common methods

• Triangulated Irregular Networks (TINs)

• Gradual or abrupt?

• Exact or approximate?

• Local or global?

• Deterministic or stochastic?

Geostatistical analyst

• Geostatistical analyst in ArcMap

Practical exercise

Hands-on Exercise #2Interpolating point data in ArcGIS