There is no generally accepted definition of the difference between
a map and a
chart. A widespread feeling probably exists favouring the old saying that
maps are
to look at and charts to work on. It is true that the term ‘aeronautical
chart’
gained a general currency over alternative terms as contact flying gave
way to
aerial navigation. But, in this paper, the terms ‘map’
and ‘chart’ will be used
as seems appropriate to each occasion, without attempt to conform to any
particular definition.
We can get an idea of what was available to the earliest aviators by
looking at
an Ordnance Survey reprint of one of their nineteenth century maps (Fig.
1).
They are printed in one colour only, black on white. By far the predominant
feature is the hill shading. Quite gentle hills are hachured with a heaviness
which
tends to obscure both natural features like rivers, lakes and woodlands
and man-made constructions such as towns and villages, roads, canals and railways.
Hills
are, of course, very important features to those on the ground, since they
limit
the extent to which other features can be seen. To the soldier, the significance
of high ground is self-evident, and it was principally for the ordnance
requirements of soldiers that these maps had been developed. But when men
began to view the ground from the air, the perspective changed. Hills appeared
flattened out and, provided that you knew the height of the tallest in
the area
and were sure none would impede your take-off or landing, were of minor
significance. Lakes and woods, though, were spread out before you in their
distinctive shapes, while railway lines and canals presented bold straight
lines and
curves, and rivers their unique courses, to your view. The need was for
new
kinds of maps which would give due prominence to such features.
