GRADES AND LEVELS 57 
the land under survey to be submitted to an 
inundation, every rise in the waters of one 
foot shows a water mark on hills and knolls 
that is at exactly the same level everywhere, 
all the way around. The wavy, irregular 
contour line on a topographical map represents 
the plan of such a water mark; and each one 
foot rise narrows the remaining portions of 
“ dry ” land and widens the spread of the 
(imaginary) waters, until at last only little 
islands remain here and there, whose topmost 
heights are something less than a foot above 
the last rise. Obviously, where a slope is very 
steep the contour lines fall very close together 
when seen from above; where it is gradual, 
they widen out. 
Working on such a plan of the ground itself, 
the plans for the house and for the garden 
may be adjusted perfectly; terrace levels may 
be calculated and terrace outlines fixed to take 
advantage of every gradation and variation. 
And though there is always of necessity a cer- 
tain measure of excavating and re-establishing 
of disturbed earth coincident with building, 
and some grading is imperative, these are re- 
duced to the minimum through the exact ad- 
justment and calculation possible. Moreover 
fhe form and size of garden divisions depend 
