The map was digitized in geographic projection, which simply takes latitude and longitude as coordinates on a flat surface. This ensures easier conversion into any other specific projection. The drawback is that distance and surface are increasingly exaggerated as we move toward high latitudes, which gives a biased view of vegetation schemes in these areas. The adequate projection depends on the scale and the extent of the area of study (global, hemisphere, continental, regional, etc.), and on the spatial analyses that are to be done (distance or area computation, least-cost paths analysis, etc.). Numerous experts have recommended specific projections depending on the tasks to be achieved. Readers can consult the extensive literature on the subject to find recommended least-distorted projections for specific areas (e.g. Bugayevskiy and Snyder 1995; Steinwand et al. 1995).
The extent most often used for global map display is -180;+180 decimal degrees. For LGM maps, this has the disadvantage of separating the Bering Strait features into the far western and eastern sides of the map. This may not matter for a simple display, but it becomes problematic when one needs a spatial contiguity of that region for dynamic studies (e.g. species replacement, population migrations, etc.). For that reason, the map is also available in an extent that allows for that spatial contiguity, which is -25;+335 decimal degrees.
Vector maps were then exported into Enhanced Postscript format (colour or black and white) and TIFF image format (colour or black and white). Besides the global maps, regional maps were also produced in these three export formats. We believe that these various forms of output will greatly facilitate the import and the use of the vegetation maps. The maps are available for download in these various formats from the Download Page.
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Last updated: Mon Dec 3 2001