# 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 = ( Σ 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:

Assuming As Ats and Vs shown below, PARS calculates Vt as follows:

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

Source: modified from Ballard and Schut, 1995