Distance from rivers
ArcView was used to assign to each cell corresponding with the distance
to the nearest river.
Rivers are used both as a water source and transport route and as such
in the past have influenced settlements patterns. Many large settlements
have built up around river ports (eg. London) and many small villages are
located at rivers crossings and near rivers themselves.
The relationship between population density and distance from river is
likely to be quite week.
It may be worth classifying rivers by their size and developing this into
a more informative layer and combine it with the distance from canals layer.