I think the keywords you need to look at are Kernel Density Estimates (or heatmaps). There are several implementations available for example
https://github.com/JuliaStats/KernelDensity.jl or KDEstimation · Julia Packages
Since you are working with a domain with complicated boundaries you might be tempted by using within DIVAnd (DIVAnd_heatmap). GitHub - gher-ulg/DIVAnd.jl: DIVAnd performs an n-dimensional variational analysis of…