- Create a polyshape for each voronoi cell.
- Loop over cells and test isinterior for each, you can short circuit when you find a match. To be even smarter, you could calculate distance to each cell's centroid using pdist or hypot, sort it ascending, and start testing isinterior in that order.
NOTE: You should really project your lat/lon data into a cartesian coordinate system. Lat/Lon are measured on the surface of a sphere so the lengths of the voronoi cell edges are not in a linear unit. Look at mfwdtran or https://www.mathworks.com/help/map/ref/map.rasterref.geographiccellsreference.geographictointrinsic.html
