22 VEGETATION OF THE PEAK DISTRICT [cH. 
Each of the succeeding chapters deals with a group of 
associations, not necessarily with a formation. The associations 
are analysed; and, as far as is possible, each association is 
then referred to the formation to which it belongs. 
VEGETATION MAPS AND FLORISTIC MAPS 
Vegetation maps indicate the occurrence and distribution 
of plant communities. Floristic maps may be of two kinds: 
they may indicate the occurrence and distribution of single 
species or of groups of geographically related species. The 
former maps are of the type which H. C. Watson (1832, etc.) 
began to construct of the species indigenous to the British 
Isles. They are very useful maps in their way, as may be seen 
by the use to which they are put in Praeger’s recent Flora of 
the West of Ireland (1909: figs. 4, 5, 14, etc.). Such maps, 
however, do not lend themselves to any generalized carto- 
graphical scheme, because almost every species requires a 
separate map to show its distribution. They bear the same 
relation to vegetation maps that a series of cartographical 
representations of erratic boulders would bear to a modern 
geological drift map. Floristic maps illustrating the distribution 
of geographically related species can hardly be said to exist as 
regards the British Isles; but Flahault (1901) has constructed 
such a map of France, and more recently Massart (1910) has 
published maps of Belgium on somewhat similar lines. 
The so-called “botanical maps” illustrating numerous 
British county and local floras are neither floristic maps nor 
vegetation maps. The typical maps accompanying these floras 
simply show divisions of the county into “drainage districts” 
or other topographically convenient districts; and no attempt 
is made on such maps to show the occurrence and distribution 
either of plant communities or of floristic groups of species. 
THE VALUE OF VEGETATION Maps 
Vegetation maps have the same value to botanists that 
geological maps have to geologists. Just as geologists may, 
by consulting geological maps, know where certain geological 
phenomena may best be studied, so botanists may, by consulting 
vegetation maps, know where certain ecological phenomena 
