Available Zoom Levels
Zoom level 0 is the most zoomed out zoom level available and each integer step in zoom level halves the X and Y extents of the view and doubles the linear resolution.
Google Maps was built on a 256×256 pixel tile system where zoom level 0 was a 256×256 pixel image of the whole earth. A 256×256 tile for zoom level 1 enlarges a 128×128 pixel region from zoom level 0.
As correctly stated by bkaid, the available zoom range depends on where you are looking and the kind of map you are using:
- Road maps – seem to go up to zoom level 22 everywhere
- Hybrid and satellite maps – the max available zoom levels depend on location. Here are some examples:
- Remote regions of Antarctica: 13
- Gobi Desert: 17
- Much of the U.S. and Europe: 21
- “Deep zoom” locations: 22-23 (see bkaid’s link)
Note that these values are for the Google Static Maps API which seems to give one more zoom level than the Javascript API. It appears that the extra zoom level available for Static Maps is just an upsampled version of the max-resolution image from the Javascript API.
Map Scale at Various Zoom Levels
Google Maps uses a Mercator projection so the scale varies substantially with latitude. A formula for calculating the correct scale based on latitude is:
meters_per_pixel = 156543.03392 * Math.cos(latLng.lat() * Math.PI / 180) / Math.pow(2, zoom)
Formula is from Chris Broadfoot’s comment.