1. A method implemented by a computer for generating an image on a display that comprises a plurality of pixels, the image representing a plurality of transactions as lines connecting points in the display indicative of a source and an origin for the respective transactions, the method comprising: successively rendering lines representing each of the plurality of transactions into an image buffer, the rendering comprising: for each of the lines, using an anti-aliasing process to determine a coverage value for each pixel of the display, the coverage value representing the extent to which the line covers each pixel; and within the image buffer maintaining a record of a cumulative coverage value for each pixel of the display; and when the lines representing each of the plurality of transactions have been rendered into the image buffer, determining a maximum and a minimum of the cumulative coverage values stored in the image buffer, scaling the cumulative coverage value for each pixel based on the maximum and minimum cumulative coverage values, and rendering each pixel onto the display by using the scaled cumulative coverage value to determine a transparency for the pixel.