I was recently given a .csv containing the locations of all recorded bicycle accidents in Boston over the past few years. As an avid cyclist, I'd like to create a simple contour map that draws attention to the intersections with the greatest accident densities to share with friends and city officials.
Using the Heatmap QGIS plugin and GDAL's contour tool, I succeeded in creating an aesthetically pleasing map, but my concern is that the numerical values of these contours are somewhat meaningless – or at least, are not particularly practical. (To my understanding, these values are related to the "elevation" values generated by the heatmap, but I'm not quite sure what the actual units are, or how to reflect them in the legend.)
I'd like to create contours that reflect the number of crashes within 400m of a given point. (So for example, any point within the highest "elevation" contours is within 400m of at least 8 crashes, while any point within the lowest "elevation is within 400m of at least 1 crash.) Is this possible? Or is there another, better way to visualize point densities using contours?
If it's any help, I generated my heatmap with a radius of 400m, a decay of 0, and X and Y values of 10 (so each cell is 10m x 10m). I converted the heatmap into contours using an elevation value of 1.
I'm relatively new to GIS, and I'm not sure if this inquiry makes much sense, but I'd be grateful for any tips or solutions to my quandary.