ABSTRACT
The first columns of Table 12.4 show some data based on map measurements of distances between randomly chosen pairs of points in Sheffield (see Gilchrist (1984)). The straight line distance is measured with a ruler (the crow flies distance,
x
) and the shortest distance by road is also measured on the map (the car distance,
y
). The objective is to find a simple relationship between the two so that
y
can be predicted from
x
. The units were measured in cm on a 1:25000 map, i.e., the unit was a quarter of 1 km. Several features follow from a general conceptual modelling argument:
(a) When
x
= 0 then
y
= 0. (b) The model must give
y
≥
x.
