Interpolating Measure Data

In interpolating measure data, the area of the source polygon is irrelevant, but the area of the target polygon is used to arrive at the target value.

Formula

For measure data, the value for each target polygon is estimated by converting the measure values to their equivalent count values for each target/source intersection. These values are summed for each target polygon, and then converted back to a measure value by dividing by the area of the target polygon.

	Vt	=	( Vs * Ats ) / At
where:
	Vt	=	value of the target polygon
	Vs	=	value of the source polygon
	Ats	=	area of the intersection of the target and source polygons
	At	=	area of the target polygon

Non-areal proportions require special treatment.

Example

Consider the following coverages:

Source polygons	Target polygons
Target-Source intersections

Assuming V_s A_ts and A_t shown below, PARS calculates V_t as follows:

Source values (Vs)	Target values (Vt)

target polygon	portion	Vs depth (m)	Ats area (ha)	Vs*Ats (m*ha)	At area (ha)	Vt depth (m)
Polygon 1	1A	1	600	600	750	1.20
	1B	2	150	300
Polygon 2	2A	1	400	400	1250	1.68
	2B	2	850	1700

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Source: modified from Ballard and Schut, 1995 by Peter Schut
Contact: Head, CanSIS