Geoscience Reference
In-Depth Information
FIG
4.
Examples of the three levels of division adopted in the treatment of Southern Eng-
land.
Maps displaying patterns of elevation of the countryside above sea level are an
important part of the discussions. The elevation data on the maps in this topic have
been compiled and made available as part of the LANDMAP project, which provides a
computer-based digital survey of Britain for research and educational use. LANDMAP
Digital Elevation Maps (DEMs) are based on satellite radar survey measurements
which divide the land surface into a grid of 25 m by 25 m pixels. The average height
of each pixel is then measured to produce a terrain model with a vertical accuracy of
about ± 5 m. A standard colour shading scale is used to represent heights, ranging from
greens for the lowest ground, through yellows and browns, to greys for the highest
ground. It is best to use the full range of colours for each map, no matter what numer-
ical range of heights is involved. This makes it possible to convey the fine detail of
slopes etc., whether the map is for the Fens or the high moors. To make it possible to
compare between maps using this colour scheme, we have quoted the maximum elev-
ation reached in each Area on each map.
I have used ESRI ARC Geographic Information System (GIS) software in the pro-
cessing and manipulating of the map data. This software makes it possible to present
artificial hill-shading, which makes the topography easier to understand, and to provide
maps representing slope patterns in certain areas.
In addition, data on roads, railways, coastlines, town boundaries, rivers, etc. suit-
able for reproduction at a scale of 1: 200,000 has been made available by the Collins
Bartholomew mapping agency. For any further details of the areas covered, it is recom-
mended that Ordnance Survey
Landranger
(1: 50,000) maps are consulted.
LANDSCAPE CHANGE
We tend to think of rural landscapes as unchanging features of our surroundings,
in contrast to the man-made scenery of cities and towns. Yet we all know of local cata-
strophes, such as a sea cliff collapsing during a storm, or a flooding river removing its
