Generalizing digital elevation models for small scale hypsometric tinting

This paper describes an automatic procedure for deriving worldwide small-scale hypsometric layers from digital elevation models. A custom generalisation procedure was developed to remove unnecessary details from the elevation model: (1) the elevation data are filtered with lower and upper quartile filters, (2) a drainage network is extracted from the elevation data, (3) the drainage network is simplified with a custom algorithm that removes the shortest streams, (4) a series of buffers are applied to the generalised drainage network, and (5) the buffered drainage network is used to combine the grids filtered with upper and lower quartile filters. After these five steps, the hypsometric layers are derived with a contouring algorithm. The proposed procedure follows the main guidelines for cartographic relief generalisation and the graphical quality of the resulting hypsometric layers is comparable to manually generalized layers.