Site mapping techniques

1. By Victor A. Spooner

2. This presentation was written for viewers
possessing some familiarity with environmental
site-assessment fieldwork activities, as well as a
basic understanding of the use of map scales,
legends, and drafting tools. Owing to these
presumptions, the resulting slideshow is almost
exclusively text based. An attempt was made to
concisely and clearly describe a few of the more
important techniques used to draft an accurate
site map from scratch, and the hope is that it is
successful in those respects.

3.  Measuring Wheel
 Measuring Tape (100’ plastic-tape variety)
 Graph Paper (8.5” x 11” with 4 blocks/inch, or
your preference)
 Clipboard
 Engineer’s Scale Ruler (1:10 – 1:60)
 Drafting Compass
 Directional Compass
 Mechanical Pencil
 Eraser
 Drafting Triangle with 90-degree angle

4. Mapping Tools, continued…

5. There are a variety of ways to draw a site
map to scale, including: use of GPS
techniques; adaptation of detailed aerial
photos; adaptation of as-built construction
plans, etc. But one of the most accurate
methods involves manually drafting your
own map in the field. To describe the
mapping process, let’s pick a moderately
detailed environmental-assessment site in
an urban area. A good example is a corner
gas station with a convenience store, gas
pumps, underground storage tanks, large
overhead canopy, parking lot, monitoring
wells, and adjacent streets and sidewalks.

6. Figure out the scale you will need to
use to best fit the map onto your
graph paper. Do this by rolling your
measuring wheel straight across the
longest direction of the site lot (end-to-
end, across any sidewalks, and up
to the edge of roads, if any); and
then do the same across the shortest
direction. This will give you the
overall length and width of the site
you wish to map.

7. Assume the site’s long dimension is 410 feet, its short
dimension is 260 feet, and that we want to draw the
site map onto an 8.5” x 11” piece of graph paper. To
fit the map with a little room to spare, we should
probably pick a map scale that uses no more than 10”
of the paper’s length, and no more than about 7.5” of
the paper’s width. Ignoring units of feet and inches,
respectively: 410 divided by 10 = 41. Using that
number, and by laying an engineer’s scale ruler across
the long dimension of the graph paper, we can see
that the 40-scale ruler edge (1”=40’) will work nicely
for our map: it will use most of the space on the
paper, allowing us to draw the map as large as
possible in that space, and will also leave us a little
room on the edges. So, restated, we just selected 1”
= 40’ as our map scale. Conveniently, in this case,
each block on the graph paper happens to represent
10 feet at this scale.

8. Next, draw the perimeter of the site onto
your map. (We will assume a
rectangular lot, so the mapped site
perimeter will be rectangular, with four
sides and four corners.) Remember
that our initial length and width
dimensions included going across
adjacent sidewalks to the edges of
roads bordering the site, so include the
sidewalks and road edges (i.e., curb’s
edge) when mapping the site perimeter.

9. Map the building by using a cool trick to orient the
building onto the page. Pick any wall of the
building; pretend that the wall extends all the
way to a nearby edge of the site (which you
already mapped in Step 3); and then walk away
from the building to that edge on the site
property that the extended wall would intersect.
Try to straddle the exact spot on the site
perimeter that the line of the wall would cross.
You can find that spot exactly by moving slightly
left-and-right until you make the wall just barely
disappear from your view. When it just barely
disappears, you are staring straight down the line
of that wall.

10. Next, on the ground, use something to
mark the spot you are straddling, and
then, using your measuring wheel,
determine the actual distance along the
site perimeter, from that spot on the
ground, to the nearest corner of the
rectangular lot. Then, after completing
that measurement, use the 40-scale of
your ruler to put a dot on your map’s
site-perimeter line that exactly
corresponds to the spot you marked on
the ground.

11. Straddle your ground spot again; move slightly to make your
wall barely disappear once more; and use your measuring
wheel to next measure the actual distance from your ground
spot to the corner of the building where your wall actually
ends. Keep the wall that you are aligned with just barely
“disappeared” to ensure you are walking and measuring in a
straight line as you roll the measuring wheel toward it.
Convert the distance using the 40-scale ruler. If it is
obvious that the building’s four walls are individually
parallel to the four sides of the site’s perimeter, then you
have it made: on the map, place your 40-scale ruler on the
perimeter dot so that the ruler lies exactly perpendicular to
the perimeter line; then use the converted distance
stretching from the perimeter dot to the building corner in
order to make the dot which represents the corner.

12. Once the building corner is properly
mapped, simply use the measuring
wheel to determine the actual length
and width of the building, convert
those lengths to map scale, and, from
that point, while remaining parallel to
the sides of the site, use your ruler to
draw all four walls of the building onto
your map.

13. Note: if the building’s walls are not parallel with the
sides of the site perimeter, then repeat steps 4, 5,
and 6 to also determine the opposite corner of the
same wall, and mark it with a point on the map.
Connecting the two map points with a line properly
orients the wall on the site map. Afterwards, simply
measure the buildings sides with the measuring
wheel, and convert to scale. Confirm the length of
the original mapped wall (it should be correct), and
then use the remaining measurements to draw the
three adjoining walls (two perpendicular and one
parallel). Use a 90-degree drafting triangle, if
needed, to draw in the other three walls.

14. Once the building is properly mapped on the page, it can
be used to orient most other site features close to the
building, like gas pumps, monitoring wells, etc. For
example: from each of two building corners, use your
measuring tape, or your measuring wheel, to separately
determine the bee-line distance from each building
corner to a particular nearby monitoring well. Next, take
your drafting compass, spread it open the proper distance
against the 40-scale ruler, and then draw an arc from the
mapped building corner toward the direction of the well.
Repeat the same compass trick from the other corner of
the building, using the proper length and compass
spread. The monitoring well will be exactly located where
the two arcs intersect. Of course, by properly measuring
parallel and perpendicular distances with your measuring
tape or wheel, you can use any building corner, or any
measured point on a building wall, as a means of
determining mapped positions of wells and other features
(without drawing arcs).

15. Once the site features are all mapped (including, if
you wish, dashed lines representing any large
overhead canopies), you can use your directional
compass to help draw in the map’s North arrow.
Often, commercial buildings are constructed with
walls parallel to compass directions, but not all
are. If the walls are not oriented N-S and E-W,
then put your back to a building corner; move
the compass until it points North; observe a site
feature that the North arrow points to; and then
draw the North arrow in a convenient place such
that it would intersect that particular site feature,
if extended far enough.

16. Put the site name on the map;
draw the map legend with all
proper symbols (monitoring
wells, etc.); and draw the 1:40
scale bar on the map.

17. Ink in all the pencil lines to
finish your map. Woo hoo!
You’re done.