Tip: pick which location the map controls with the radio buttons above, then click the map or drag a marker. Date range is arbitrary (older than ~3 months uses the historical archive).
Pan & zoom the map to the area you want, pick a date range, then “Sample this view”. The grid is sampled across the current viewport and coloured by daily maximum temperature. Finer grids issue more requests; large grids (50–100) can hit the public Open-Meteo per-minute limit — use the unthrottled Self-hosted source for those, or shorter date ranges. “Exclude water” drops open-sea cells (elevation 0) from the map and the land average.
Sample a viewport to build a heatmap.