Topographic Maps and Digital Elevation Models

Chapter 6 Topographic Maps and Digital Elevaton Models 97
also important if you plan on taking a
GIS class in the future.
Map Coordinates
and Land
Subdivision
Coordinate systems provide a permanent
way of describing locations. For example,
older descriptions of mineral or fossil sites
commonly refer to landmarks. Unfortunately,
some of these old sites are now lost
because road intersections, houses, small
bridges, old trees, and railway lines have
since been moved or removed due to
ongoing development. A coordinate system
allows a state to efficiently and pennanently
keep track of the locations of abandoned
oil wells, toxic waste sites, sealed
mine shafts, and places hosting endangered
plants or breeding pairs. It allows
geologists to describe important rock
localities, and it allows hikers to precisely
locate trailheads, remote camp sites, and
other places worth remembering.
Latitude-Longitude
System
The most well-known global coordinate
system is based on east-west lines called
lines of latitude and north-south lines
called lines of longitude.
Latitude measures distance north or
south of the equator. The lines of latitude,
also called parallels, form a series of parallel
circles running east-west (horizontally)
around the globe. The equator represents
the 0° latitude line. Other parallels
are set at angular intervals measured
north or south of the equator, as shown in
Figure 6.5A. A latitude line 40° north of
the equator is termed 40° N. The geographic
poles are at 90° and 90° S.
Longitude measures distance east or
west of the Prime Meridian. Lines of longitude,
also termed meridians, form a
series of circles running north-south (vertically)
and intersecting at the geographic
poles. The Prime Meridian is the northsouth
line passing through the Royal
Observatory in Greenwich, England; it is
defined as 0° longitude. The other meridians
are set at angular intervals east or
west of the Prime Meridian, as shown in
A.
Equator