Imperviousness, which is defined as the property of a surface that prevents infiltration, is directly a measure of urbanisation. This is mainly due to the fact that the built-up area as a result of urbanisation contributes to imperviousness. The current study uses a remote sensing technique along with the available geographic information system (GIS) data to determine the imperviousness characteristics of an urban catchment. The objective is to quantify the difference in imperviousness determination due to spatial resolution of satellite imagery and to suggest any corrective measures for improving the methodology. The results indicate that impervious classes are found to be underestimated and vegetations are overestimated in low-resolution Landsat images due to the presence of sparsely located hilly settlements. Impervious areas that are underestimated were correctly traced by the use of building footprints for the area, which also prevents overestimation of the pervious group. The study clearly indicates that urbanisation defined based on imperviousness can be underestimated, if fine-resolution satellite imagery and suitable methodology is not used. It is recommended to use the best possible fine-resolution imagery available integrated with the GIS dataset for the precise determination of imperviousness and quantification of urbanisation growth.