Understanding zoom levels

Boyd’s Maps consist of many small 256×256-pixel tiles that are stored on the server. This makes map access fast, since the server only needs to find the right tiles and send them to your web browser. Each zoom level has its own set of tiles and the highest resolution tiles for a map are known as its maximum native zoom level. This varies, depending on the map – for example, LIDAR in the Pines HD has a maximum native zoom level of 17 but Cook’s Map of the Pines has a maximum zoom of only 15. At the maximum native zoom level, every pixel in the original image will equal one pixel on your screen. But it’s easier to see small details by zooming in farther (this is called over-zooming), so the maps are configured to let you go several clicks beyond the maximum native zoom level. You’ll notice a drop in image quality as you over-zoom the map.

Using pre-compiled tiles works well for maps of a small area such as the New Jersey Pine Barrens, but this approach isn’t practical for larger maps that cover a big state like New York or Pennsylvania. So map tiles from these sources are generated on-demand as you access the map. The server scales and crops a big image into the little tiles that you need, which requires a lot more processing power and generally results in slower map rendering.

If you create a link to an over-zoomed view of a map, in most cases it will be automatically reduced to the map’s maximum native zoom level when somebody clicks that link, however they will be able to manually over-zoom the map.

 

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