The earth’s graticule and Projections 97
tem because the zones are smaller. Because the zones are small and because they are
based on states the SPCS is not useful for national and regional mapping.
The SPCS, like the UTM, is based on zones, but these generally follow political
boundaries so the map of zones appears more irregular. The number of zones in a
state depends upon the size of the state; the boundaries within a state follow county
lines except in Alaska. The SPCS uses about 120 zones to cover the United States.
Like the UTM, eastings and northings are used, which are distances east and west of
the origin. The origin is usually 2,000,000 feet west of the zone’s central meridian.
U.s.
Public Land survey system
The U.S. Public Land Survey System (PLSS) was first proposed by Thomas Jefferson
and implemented shortly after the end of the Revolutionary War. Two ordinances,
the Land Ordinance of 1785 and the Northwest Ordinance of 1787,
provided for
systematic rectangular survey of federal lands so that
those lands could be trans-
ferred to private citizens. The PLSS is a
cadastral or property-mapping system. Not
all states are covered in the PLSS because it provided for survey before settlement.
Thus, the original colonies are not covered, and Texas has its own system (Figure
6.7). The PLSS was initially begun in Ohio, but because the system was not yet fully
developed, the surveys in Ohio and Indiana are different from those of other covered
states. There are also some areas where other cadastral systems were in use, such as
Louisiana, which used the French
arpent system, or long lots; New England, which
used the New England town system; and areas of the Southwest, which used Spanish
systems.
The PLSS is based on 37 named principal meridians and base lines, as shown
in Figure 6.7 that provide origins. True north–south lines (meridians) and east–west
lines are drawn from these origins at 6-mile intervals called “tiers and ranges” (while
I
II
III
IV
V
VI
California State
Plane Coordinates
