Current practice in building simulation is to use historic climate data which has been measured in rural locations. However, numerous measurement programs have demonstrated that the urbanrural temperature difference can be of several degrees Kelvin, with corresponding implications for heating/cooling energy consumption in buildings. In order to quantify this issue for a specific case, we study the city of Madrid (for reasons of data availability). In this we simulate the region for the case in which the city is physically represented as well as for the case in which this is artificially replaced with a rural representation. We then produce spatial maps of degree hours of cooling for the two scenarios and the summertime period in question; and from this a quotient image. Using these results we discuss implications for cooling energy use.