Using software to calculate difficulty of a route

@izogi Continuing from 'sections' discussion: Yes - a generic solution that models the entire area and lets you calculate the cost of ANY route across it would be preferable to a one-off calculation for known tracks in the Tararuas. I'll try and have a play with this problem Izogi. I'm sure it has been solved before. The usual way these calculations are addressed is by creating a 'cost surface' or 'friction surface' - basically a grid containing a value for the difficulty of traversing each cell in the grid, based on a weighted combination of one or more variables. These are easy to generate and easy to use. However in this case it's a bit more complicated - as whilst some 'friction' variables are simple numbers (e.g. vegetation type or track type) the slope is vector variable (it has both a steepness and a direction) and the direction you travel across a cell strongly changes the impact the slope has on you. Most GIS packages will let you convert a DEM (elevation model) into a (slope,aspect) model, containing 2 values for each grid cell - the steepness and the direction. However, I've not seen any built-in routines to calculate the effect of such vector variables on someone travelling across the grid. Implementing it in custom code would be quite easy though, as it's a simple calculation as once you know the direction of slope and the direction you are travelling in you can work out the proportion of the slope that affects your track. I'll get back to you if I find a ready-made answer though.