I'm struggling to produce a map as follows:
Basically, I am using Google Map APIs (JavaScript) to visualize my data. My data contains plenty of points. Each point has coordinates (lat, lng) and a value (pollutant). I've tried to use heatmap layer in Google Map but it looks ugly compared to this image.
Here is my output using heatmap:
So my question is what software/package/library can make the first picture? Many thanks.