A 1-hectare parcel across British National Grid, at 52°N
The departure of a plan's dimensions from the ground's, across the width of the zone, as a length and as an area. The area curve is the length curve doubled — an areal scale factor is the square of a linear one, and squaring a small departure doubles it — so a parcel whose sides are each 399 parts per million short on the central meridian is 797 short in area. On a 1-hectare parcel that is 8.0 square metres at the central meridian and 8.0 at 0.00° out.
It is drawn by survey-figure with
show: "parcel-area" — one member of a family of
16 figures
that share a generator, so the drawing above is what that generator returns when it is asked
for this one and given nothing else.
2 essays call it. Every call below passes it something, because a placement that passes nothing draws whichever member of the family the generator happens to default to rather than the one its essay argues about.
Where it is called
Changing this changes every one of these figures.
Grids, and what a survey does
An area on the grid is not an area on the ground
A grid's scale factor is a property of lengths and what a surveyor sells is an area. Squaring a departure doubles it, so a hectare drawn on the British grid at its central meridian has 10,008 square metres of ground under it — and correcting an area with the line factor instead of its square leaves half the error behind.
What a machine does with it
A thousand features are wrong in the same direction
The area a simplification costs is unpredictable in sign for one feature. Over a population it is not: twenty-four presentations of one shape all lose area, the mean is seventy standard errors below zero, and no amount of aggregation removes it.