Interpolating Count Data

In interpolating count data, the area of the target polygon is irrelevant, but the area of the source polygon is used in the calculation of the target value.

Formula

For count data, the value for each target polygon is estimated from the value of each intersecting source polygon multiplied by the area of intersection as a fraction of the area of the source polygon.

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

Example

Consider the following coverages:

Source polygons (As)	Target polygons
Target-Source intersections (Ats)

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

Source values (Vs)	Target values (Vt)

target polygon	portion	Vs (cows)	Ats area (ha)	As area (ha)	Vs * Ats / As (cows)	Vt (cows)
Polygon 1	1A	100	600	1000	60	90
	1B	200	150	1000	30
Polygon 2	2A	100	400	1000	40	210
	2B	200	850	1000	170

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