In one aspect, the present invention relates to a method of determining the sky-view factor at a location. The method comprises the steps of receiving data from at least one global positioning satellite at the location, and comparing the data so obtained with a mathematical function. The function is derived from corresponding data obtained from reference locations at which the sky view factor is known, whereby to arrive at an approximation of the sky view factor at said location. In another aspect, the invention relates to a method for predicting the variation in temperatures over time at locations along a survey route, particularly a road network. The method comprises the steps of establishing a database for the survey route containing location specific geographical parameters, obtaining actual and forecast meteorological data and separately predicting the temperature at each location using energy balance equations. The predicted temperature calculated for each location is dependent upon the meteorological data and the geographical parameters for the location whose temperature is being predicted. The invention also discloses systems which relate to the above methods.