point I hope that you are aware of your requirements
With these figures you now have the
basis to form a design in your garden so you need a site plan.
One of the best tools for surveying
is the eye. Carrying out a good visual survey is the most useful method
of surveying - it can also be misleading. Without a visual horizon it
is easy to get levels wrong. A large flat lawn can appear absolutely
level and even walking over it could feel level but it could quite
easily be on a slope which would make even big engines struggle.
Producing a Survey
Professional engineers nowadays will
do this by establishing at least two known points with co-ordinates.
Co-ordinates are denoted in three fields - Eastings, Northings and
height. Then using a total station (an electronic instrument that
measures angles and distances) they would take co-ordinate readings of
identifiable objects such as building corners, road edgings, fence
posts, boundary lines and spot levels.
From these coordinates the engineer
is then able to draw on a computer a scale plan, complete with contour
lines and points with heights. For our purpose I am assuming that the
majority of us do not own or have access to a total station or
theodolite and therefore need to carry out a survey using a more
For our purposes and resources this
is the simplest method of land surveying. Traditionally a measuring
chain would be used. The two types of chain would be an engineers chain
at 100' long with 12" links and a Gunters chain 66' long with 7.92"
links. Incidentally, ten square gunters chains equals one acre.
A 30 or 50m tape measure will not
cost too much and is a lot easier to use than an old chain. Other than
the equipment the method used to carry out a land survey has not
changed in centuries.
The basic principle is based around a
triangle. Once the lengths of the three sides of a triangle are known
it can be reproduced on paper at any desired scale using the simple
instruments of a scale rule and a pair of compasses. For mapping out a
garden you would position a triangle with one side as nearly parallel
as you can get to a boundary or building. By measuring the triangle and
the short offset distances from the lines the garden can easily be
plotted. For most gardens more than one triangle would have to be used.
The offset distance is the distance
from one of the lines to any given object. This is measured at a right
angle to the line using a tape measure. The right angle is judged by
eye and therefore should only be used for shorter distances usually the
length of a pocket tape measure is enough.
If you do need to measure a further distance a right angle can by found
by using a 3 4 5 triangle.
|A triangle with
sides of 3 4 5 will have a right angle on the intersection between the
lines 3 and 4. Therefore if you measured 800mm along the off set line,
600mm along the measure line then hold a measure out from this point
with 1000mm length were the two intersect will give you a right angle.
For our purposes the
easiest and clearest method for recording the readings is to draw a
quick sketch of the whole area to be surveyed. The triangles used can
be roughly drawn and the lengths of their sides written on. The offset
readings can also be written on complete with a sketch or note of where
it is taken from.
Although it will look
nice a complete and detailed sketch of the garden, it is not really
necessary. Only the objects which may affect the proposed railway need
to be accurately plotted. Items such as trees and paths which are some
way away from any potential construction can be drawn with a bit of
guess work and free hand sketching. If there is the slightest chance
you may extend into these areas then take that little extra time while
you have the equipment.
In drawing your plan you
first need to choose a scale which will fit on the page. Once you have
done this start plotting the main triangles using a pair of compasses
and a scale rules. By using the measurements from your sketch you
should start to see the outline of your garden start to take shape.
can then be drawn in by free hand. If, for example you took
measurements of a path at 1m intervals, you can draw in the path to
some degree of accuracy by simply drawing a free hand line which
dissects your plotted points.
Once all the details are
completed rub out all the triangle and offset lines and ink over all
the details which you want to keep. At this stage it is worth making
several photocopies which you can then work from. Using the scale ruler
and a pair of compasses any proposed route can be simply plotted on to
|This only produces
a dimensional plan and does not take into account of levels. If you
have a garden with a steep slope measurements should be taken by
holding the tape measure level. Where there are large steps a pole can
be used to mark the end of one tape and the start of the next.
As in the above
diagram, if you measured the direct line from A-B you would not get the
horizontal distance of 50m but instead 50.249m - an error of 249mm
enough to throw out the best laid plans.
Ground levels are also a large influencing factor on design and a
proper level survey needs to be carried out.
Next Stage - Level