MAPPING AS AN ECOLOGICAL INSTRUMENT. 
727 
represents an association in which the three are equal in 
distribution. By a judicious combination of letters and 
brackets it is possible to illustrate a great variety of 
associations in a very simple and concise way. Multiplicity 
of associations on a single map is to be avoided if possible — 
it is usually practicable to select a few typical combinations 
into which most of the associations can be fitted. 
One of the great essentials for the success of a field map, 
apart from actual accuracy in working, is neatness of charting. 
A very hard, sharp-pointed pencil is required, 3 H being the 
softest that can be recommended, and the lettering on the map 
needs to be very small but clear, in order to avoid overlapping 
and confusion. 
When the adjacent sections of the field map are completed, 
they are placed together to make certain that they fit on to one 
another accurately, any discrepancies being remedied by 
additional measurements and corrections. The whole chart is 
then inked in with Indian ink for the sake of permanence, and the 
completed map is finally transferred on to tracing cloth, giving 
an initial map in a form that is convenient for working purposes 
in the field. 
In order to show more clearly the relations between the 
various associations of plants or between the different types of 
soil, a blocked-in map can be constructed from the preliminary 
one. For this the outlines are traced, but instead of the letter- 
ing being transferred, the areas of the associations, for instance, 
are blocked-in in various ways. On Blakeney Point the 
distribution of Suceda fruticosa is a very outstanding feature, so 
in the blocked-in map this plant is represented by solid black 
colouring. The Salicornia marsh is dotted, and as the “ Aster 
Tripolium ” field is regarded as a specialised Salicornia marsh, 
it is shown by heavier dots, while the rather mixed association 
fringing the upper edge of the marsh appears 0W0 Contrast 
is the great point at which to aim, hence as sand-dunes and 
marshes are so diametrically opposite, the dunes are delineated 
by slanting lines. Care must be taken to reduce the number of 
