# Tools: DEMs¶

## Select NeXTMap tiles¶

Selects the DEM tiles from the NeXTMap project (NEODC, 2009) which are needed to cover an image. Can take an input from either a georeferenced image, a set of corner co-ordinates for an image, or the bottom left co-ordinates and length/width of an image.

### Input¶

Image co-ordinates (from one of the above options)

### Output¶

List of NeXTMap tiles needed to cover the image.

## Calculate Surface Area¶

Calculates an estimate of the 3D surface area of a DEM using the Jenness (2004) method.

### Input¶

DEM with associated map information including pixel size

### Output¶

New image band containing a ‘surface area image’ (similar to the slope and azimuth images created by the ENVI Topographic Modelling command) where the value of each pixel is the surface area of that pixel.