WHERE AND HOW

Download USGS Satellite Imagery at http://earthexplorer.usgs.gov/

Create account and either search or click map of desired area - feature.

Enter date range. 2000 - to today.

Height maps = Digital Elevation> ASTER GLOBAL DEM

High Res Colour maps = Aerial Imagery>High Resolution Orthoimagery

Click ‘Results’.

‘Show Browse Overlay’ displays a preview of the satellite image on top of the world map

‘Show Metadata and Browse’ contains dates, coordinates, etc.

THE GeoTIFF

Tile size = 1° lat x 1° long

1° x 1° = 111.699km at equator 110.567km at poles.

average = 111.133km

3601 columns x 3601 rows

pixel size = 1 arc second

1 arc second = 30.87m (? I guess this also changes)

3601 x 30.87 = 111.16287 km (? this number comes out a bit above the average)

*Either stick to average or use Area by Lat Long coordinates for exact measuments)

16bit TIFF with 65,536 levels of grey and -9999 levels for voids (Ocean, caves etc)

Sea level = 9,999 grey.

So for land elevations relating to sea level need to add 15.257% to remap accounting for voids. (9999/65536x100)

Inherent 95% accuracy with 17m degree of error in height.

Which allows for a small % to add or reduce elevation in Houdini etc.