Internet Archaeology 11: Ray & Adams 3.2 Vegetation map

3.2 Vegetation map

3.2.1 Digitalization

A first set of hand-drawn maps were digitized and merged in the GIS facility of UNEP/GRID-Geneva (United Nations Environment Program/Global Resource Information Database-Geneva) using the Geographic Information System (GIS) ArcInfo 7.2 (ESRI Inc., Redland, USA). After correction of typological errors with ArcInfo, we exported the file into the GIS package ArcView 3.2 (ESRI Inc., Redland, USA), where the rest of the map production was carried out. Vegetation borders were then directly corrected with ArcView, using the standard digitizing tools. When contours were based on altitudinal zonation or past LGM coastlines, they were altered directly on screen, with the appropriate information in the background.

3.2.2 Key to vegetation types

In compiling these maps, we have tried to adhere as closely as possible to the well-known and widely cited scheme developed by Olson et al. (1983). Given the nature of the task we have, however, merged some categories and added others, including some vegetation types for the past that have no close analogue in the present world.

A key to the vegetation types under which the data are categorized can be found in Section 8. The coding numbers correspond to the numbers on the regional maps. A brief description of the physiognomy of each vegetation type is given, together with the nearest corresponding vegetation type(s) on the global ecosystems map and carbon storage database of Olson et al. (1983). Finer subdivisions of vegetation type were not mapped onto our global map, as we feel that there is presently insufficient information to allow such subdivision to be used.

3.2.3 Expressing the uncertainties in the vegetation map reconstruction

It is difficult to relay any simple measure of the amount of confidence to be placed in the patterns of vegetation distribution drawn onto the maps presented here. It has been necessary to weigh up each case according to which of the cited authors and contacts presents the most convincing set of evidence and arguments. The justification for presenting any particular vegetation reconstruction in the maps is a complex and subtle process (which can be best understood by studying the discussions in some of the individual source papers, or the online QEN database).