TRIANET | DTM - Digital Terrain Model

The original elevation data are taken from digitized contour lines. The vertical distance of the Contour lines is 100 m (that causes some problems with the quality – see below). There are 18277 original elevation data points provided by the digitized contour lines.

The regular gridded DTM was created on the base of the irregular spaced elevation data from the digitized contour lines using Golden Software’s SURFER program. For the interpolation method for the grid "kriging" was used – calculating a grid cell size of 100 m.

The quality of the DTM is sufficient for meso scale investigations in the mountain regions of Naxos. In the plains (e.g. Livadi coastal plain in the west of the island and Tragea plain in the centre) there are a lot of "artificial" elevation data in the DTM (you can see this e.g. on some "radial valley structures") which will lead to misinterpretations. These "artificial" data are caused by the great vertical distance of the Contour lines of 100 m. Some more digitized contour lines (e.g. 50 m or even 25 m) would solve this problem.

*Maps derived from the DTM*
	Analytic hillshading with contour lines This map shows two possibilities of relief visualisation based on DTM: 1. The Contour lines are interpolated from the gridded DTM. You can choose (theoretically) every equidistance for the contour lines. In the map the equidistance is 50 meters. 2. The calculation of analytic hillshading is based on the calculated slope direction and slope angle for each grid cell of the DTM. The virtual light source is located in the north west.
	Classified altitude with analytic hillshading This is another possibility of relief visualisation: analytic hill shading (see above) in combination with classified altitude (meters above sea level) shown in different colours.
	Areas with convergent and divergent surface runoff and calculated stream lines This map is an example for relief analysis - in this case aiming on application in hydrology or erosion. The visualisation is supported by analytic hillshading (see above). 1. The convergent areas (blue) are supposed to have a concentration of surface runoff, the yellow areas have divergent surface runoff and the intermediate areas neither nor. The calculation is based on slope direction in combination with the slope angle for each grid cell of the DTM. 2. The calculated stream lines are potential brook or river beds with linear runoff. The used algorithm for calculating stream lines are quite complex, simulating surface runoff (in the model the surface is supposed to be waterproof) under constant precipitation.

Note: Please remember that all derivations from DTM are based on pure altitude data. For the interpretation of the results of the digital relief analysis you need further information about climate, soils, rocks, vegetation, etc. For the example of calculated stream lines (shown above) that means: under the given climate of Naxos (rainfall nearly only in winter and high rates of evapotranspirationin summer) the stream lines will be nearly always dry. You will find there water only after heavy rainfall whereas under the climate of Central Europe you will find brooks or rivers at nearly every stream line.