- What is a contour?
A contour is a line connecting points of equal elevation to graphically display ground height.
- What is a DTM?
A digital terrain model, or DTM, is a digital representation of a topographic surface. It will not include surface features such as buildings, bridges and trees.
- What is the source of Land-Form PROFILE?
The contours were originally surveyed using photogrammetry (a means of stereo image interpretation, like 3D, using aerial photography) and supplied as published mapping. These graphic contours were later digitised to give the Land-Form PROFILE data contours we have today and from which DTMs are interpolated. This is why DTMs have a lower stated accuracy than contours.
- Why are there gaps in the contours?
These gaps are a legacy of the source material from which Land-Form PROFILE was derived. So, where the published 1:10 000 scale mapping contains breaks in the contours, such as cuttings, embankments and active quarries, these will be mirrored in the data. Contours may also be broken to improve cartographic appearance at very steep slopes, where they would have merged when depicted at scale on the original mapping.
- Which should I buy, contours or DTMs?
This is very much a personal choice and depends on what you intend to use the data for. Many proprietary software packages allow you to interpolate DTMs from contours and vice versa, so making sure you have the right system into which to load your data is important. A number of licensed partners offer solutions specifically for customers looking to incorporate height data into their applications.