Is there a word/map for the transit accessibility for each point (1m^2?) on the map and drawing that? (maybe an integral of the isochrone?) E.g. pick a point o

Is there a word/map for the transit accessibility for each point (1m^2?) on the map and drawing that? (maybe an integral of the isochrone?) E.g. pick a point on a map, sum the area of the isochrone (30minute area? weighted sum?) to get a value at that point. Then redraw a heatmap of those points.