title: How to render a lower resolution tile when the tile is missing
body: <p>I have an OpenStreetMaps map rendered via Leaflet with layers kept local, from zoom 0 to 17. Yet, I am interested in maps centered at my city, so I only have zoom 17 inside the city, zoom 16-15 inside the suburbs, zoom 14-13-12 for the state, and so on.</p>
  <p>When a tile is missing, leaflet renders a hole. I want to prevent this. I have seen sometimes rendering of lower resolution tiles in other sites. Is this just a browser cache thing? How can I render a tile at lower resolution instead of a hole?</p>