The Swiss Wind Atlas describes the wind conditions at five different altitudes: 50, 75, 100, 125 and 150 metres above ground level. The data are based on a Swiss-wide model with a horizontal grid width of 100 metres. The modelled mean annual wind speed is shown for each grid point in the atlas. Measurements recorded over a lengthy period of time were used for modelling the wind speeds and directions. Because the density of measurement points is not uniform throughout the country, and inaccuracies can thus occur in the modelling of wind flows in complex terrain, the following margins for error have been specified: Jura range, +/- 0.5 m/s; central plateau, +/- 0.8 m/s; foothills of the Alps, +/- 1.0 m/s; Alps, +/- 1.5 m/s. On maps of terrain at an altitude of more than 100 metres above ground level the number of available measurements for modelling is significantly lower, which increases the uncertainty of the results. The indicated figures should be regarded as approximate estimates of the wind conditions. Measurements directly on site are essential in order to record the development at a given location.