# Upkeep - Area difference

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SECOND DRAFT

## Background

A technical tolerance is an expression of uncertainty or precision. Such uncertainty comes from two main component:

1. the nature of the object measured, which is stable and independent from the actual measurement. It can be calculated (semi-)automatically in the LPIS for each parcel
2. the effects of the actual measurement, in case a delineation on digital orthoimagery. This component is measurement dependent and has to be entered on a case by case basis.

Assuming the second component is duly selected and controlled as one would expect for a reference parcel, only the first component is considered. The remaining uncertainty is expressed as the expected area error amplitude (EAEA)

## Procedure

The procedure for the calculation of significance of reference area difference:

• input manifest changes by type
• proceed with types I and III
(for type II changes, make Anew the new reference area and finish the procedure)
• determine the reference area for types I and III
use the EAEA formula that takes parcel properties into account
• calculate the difference |Aold - Anew|
• if |Aold - Anew| >= EAEA than the difference is significant - replace Aold with Anew
• if |Aold - Anew| < EAEA than the difference is not significant - keep Aold
• finish the procedure

figure 3dii.1: activity diagram for assessing significant area difference

## Formulas

It's scientifically possible, but rather impractical to establish the probability for each individual image, land cover feature and landscape. Rather a simplified formula is proposed.

The Expected Area Error Amplitude is then calculated as

EAEA = C(RMSp) * B [m2]

### RMSp - resolution

RMSp accounts for the map scale represented by the pixel size of the map (note that the guidelines impose a relation between GSD and pixel size, dependent on the sensor type. For CAPI, the RMSp equals the pixel size in meter

### C - shape and size

The C-value depends on the shape of the parcel (regular, elongated, irregular…). It is calculated from the Gaussian formula and is a function of the pixel size RMSp:

### B - border properties

B relates to the nature of the parcel boundary perimeter, it is estimated by the following table, based on the abundance of border quality:

 Perimeter composition >60% precise borders >25% vague borders all other conditions B value 1.96 2.94 2.45

where:

1. precise borders: those composed of ground level features that have an identification precision better than 50 cm. Examples are: crop boundaries, base of fences, base of walls, road sides,....
2. vague borders: are composed of features NOT at ground level (raised or sunk for 2 meters or more), that block visibility to the ground level and that are subject to cyclical dynamics. Examples are: Lines of threes, high hedges, deep ditches, terraces....
3. intermediate borders can be identified for border qualities which do not qualify as either precise or vague: e.g. low hedges, degraded walls.
Note: Any third party boundary (e.g. cadastral boundary, topographic map line) is considered a precise border IF it represents a physical (fence, boundary marker) rather than a virtual (legal) feature.

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