#
Globe

##
Pan and Zoom

This part describes the way MapClient implements moving around and zooming in and out of maps. The maps used are quite large, so they show a lot of detail. This is also are very fine example of advanced MapServer technologies: tiling, resampling, integration with Grass GIS, etc. It is really a marvel to see how quickly and effortlessly Mapserver manages all these big data sets. They are all from the public domain and can be downloaded for free, although some processing is required to get them into MapServer. I did this using the public domain GRASS GIS, and Frank Warmerdam's excellent GDAL utilities, which can manage every raster format known to man.
All raster maps have a grid spacing of 30 seconds (1/120 degree). Consequently, every map is 43200 by 21600 cells. At the equator one grid cell is about one km; progressing north or south cells get smaller. Uncompressed, all maps are about 1G, compressed they measure from 30M to 400M, depending on the variability of the cells.
The first example is the "Global Land One-km Base Elevation (Globe)" map
from the Globe Task team. Elevation ranges from -407 to 8752 meters, and has been colored in blue, green, yellow, brown and grey ramps.
When zooming in on this map,e.g. in Central Europe
, different levels of detail become visible (e.g. the Alps and the Rhine in the last ones), until at last the km grid shows up
. Panning works as expected, like here from Minneapolis to Mexico City
. Independently from the geographical extent, the browser window can be made larger or smaller, like in this picture from the Himalays
.