56 SUBURBAN GARDENS 
may be simple too — even though it does not 
stay on one plane all the time. But to work 
out a plan for grounds of irregular surface, 
the irregularities must be consulted and set 
down upon the drawing; otherwise the plan 
cannot fit. It is, therefore, a little less simple 
to design such a garden, and a topographical 
map is essential as a basis to work upon, if 
any great irregularities exist. 
This is getting rather too deep into techni- 
calities possibly for the average amateur; yet 
a contour map is a very simple thing, easy to 
understand and easy to work upon — and not 
indeed very difficult to make, although I shall 
not ask you to go quite as far as that. For an 
engineer’s survey should be made of land that 
varies enough to affect house and garden de- 
sign; then all the work can be planned exactly. 
Such a survey reckons usually from a level 
previously determined by the general survey 
of the town or county, but this does not matter. 
All that matters is the mark of the lowest 
level, which will be the lowest figure given, 
whatever the station may be. This mark may 
be O or anything else; but everything that is 
not on its level will be above it. 
Contours at one foot ascend from this low- 
est plane a foot at a time; that is, supposing 
