Characteristics - Landmap DTM

Resampling method

Make your mind up, 30 m or 25 m resolution!

The Landmap DTM was processed in geographic coordinates.

The resolution of the DTM during processing is 1 arc second. 1 arc second is 1/3600 of a degree. At the Equator a 1 arc second pixel in the longitude direction is approximately equal to 1 arc second in the latitude direction. An arc second equates to 1/60 of a nautical mile (1852/60 = 30.8667 meters). An arc-second of latitude remains constant while the arc-second of longitude decreases as you move away from the Equator to the poles. To work the value of the arc-second you multiply the cosine of the longitude by 30.8667. For Britain that would mean a DTM pixel in Devon would be 30.8667 m in Northing and around 20 metre in Easting while in Shetland a pixel would be still 30.8667 m in Northing and about 15.45 metre in Easting.

As we can not work with wonky pixels and that they should be square we have taken a middle point, 25 m, to represent the value of a pixel upon projection into both the British National Grid and the Irish National Grid.