The current invention relates to a computer-implemented method for creating an overlay map, preferably a heat map, comprising: receiving at a server a user request for creation of the overlay map; loading vector data at the server comprising location data, the location data comprising at least one attribute; converting the vector data to image data composed of pixels according to an index scale; applying the converted image data to a color ramp; and creating the overlay map based on the converted image data and the color ramp; wherein said vector data is organized according to a plurality of layers, the location data comprising at least one attribute for each layer.