Land-Form PROFILE ^® FAQs

What is a contour?

A contour is a line connecting points of equal elevation.

What is a DTM?

A Digital terrain model, or DTM, is a digital representation of a topographic surface interpolated from the surveyed contours. It will not include surface features such as buildings and trees. This extra information is often referred to as 'clutter' and can be found typically in a laser scanned (see question below) digital elevation model (DEM).

What is laser scanning?

Laser scanning uses an airborne laser to capture high accuracy DEMs. The system works by sending a laser pulse from an aircraft to the ground and measuring the time taken for the signal to be returned. This information combined with the precise position and orientation of the laser device when the measurement was taken allows for the production of a highly accurate DEM. One of the perceived benefits of a capture method like laser scanning is the acquisition of 'clutter' such as trees and buildings. This information is invaluable when the data is used in applications such as telecommunications line of sight modelling, flood risk analysis, insurance assessment and forestry management.

What is the source of Land-Form™ products?

The contours were originally surveyed using photogrammetry (a means of stereo interpretation using aerial photography) and supplied as published mapping. These graphic contours were later digitised to give the Land-Form 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 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 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.

Can I use Land-Form PROFILE with other Ordnance Survey data?

Yes. Land-Form PROFILE can be combined with Landplan data for example.