On Apr 20, 11:07 pm, Andrew Leach <[email protected]> wrote: > > At the equator, 1 degree is 111320m, which means that 0.000001deg is > around 11cm. Seven decimal places allows you to place a marker to an > accuracy of around a centimetre, which can't be shown on a map. >
if there's a google map with pixel dimensions smaller than this resolution of 0.000001 degrees, then we wouldn't be able to locate every pixel. That way we could show a map where 6 digits was not enough. Let's look at the typical maximum zoom of 20 on satellite maps, with pixel dimensions of 0.00000134 degrees at the equator. This is ok at the equator, but as we move towards the poles, the scale of the mercator map increases according to the secant of the latitude. As we go north, everything appears larger than it really is (like we are zooming into the map, but without changing the zoom level). This causes a problem on zoom level 20 where secant(latitude) > 1.34, which is anywhere greater than 41.7 degrees. For example Seattle, which has orthophoto aerial imagery of 10cm resolution. This is more precise than the 6 digit resolution of 11cm. If you were using google maps in Seattle to trace building outlines at maximum zoom, you would need 7 digits of precision for the latitude to be sure you could locate every pixel on the map. But 6 digits of precision would still be ok for the longitude. There are some cities with a greater zoom level of 21 for satellite maps, like Tokyo and Sydney. They would need 7 digits of precision to maintain the accuracy of the source imagery. ... -- You received this message because you are subscribed to the Google Groups "Google Maps API" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-maps-api?hl=en.
