360º make a circle
(earth is divided into 360º)
Degrees are divided up into 60
smaller units called:
Each minute is spilt into 60
To precisely locate points on the earth,
degrees latitude and longitude have been divided into minutes and seconds
(e.g., Lat:38º53’23”N; Long:77º00’27”W U.S. Capitol
Lat: 46° 52' 19.7" N, Long: 113° 59' 38.4" W Missoula, MT)
Lat: 46° 52' 19.7" N, Long: 113° 59' 38.4" W
Great…but what about the realities of declination?
Magnetic declination = the difference between true north (the geographic North
Pole) and magnetic north (the north that your compass
True North Pole (star symbol)
The geographic North Pole; the axis around which earth rotates
Magnetic North Pole (MN)
The north that your compass points to
Grid North (GN)
The direction of reference lines shown on the map
Magnetic declination = the ANGLE between True North
and Magnetic North.
* The amount of declination at any given point depends on the location
of that point on the continent.
•Where true and magnetic north are in the same direction, the
declination is ZERO.
* In North America, a line of zero declination runs from just west of
Hudson Bay, down along Lake Michigan, to the Gulf Coast in western
Florida. At any point EAST of that zero line, a compass needle will
point west of True North (called “westerly declination); in North
America, magnetic declination varies from 30° east in AK to 30° west
14° 13' EAST
For online declination adjustments:
A compass consists of a magnetized pointer that aligns itself accurately with
Earth's magnetic field. A compass provides a known reference direction which is of
great assistance in navigation. The cardinal points are north (0°), south (180°), east
(90°), and west (270°).
The composition of the earth
acts as a bar magnet sitting
upside down in the middle of the
planet. Since its South end is at
the north pole and its North end
is at the south pole, the North
end of a compass needle is
PACE = 1 natural step
PACE = # of meters or feet / # of steps
(e.g., 100 feet/25 steps = 4 feet per step)
Scale = the relationship between distance on the map
and distance on the ground.
Large scale maps
Cover large areas
1 inch = 8 miles
1 inch = 4 miles
Small scale maps
Show details, smaller areas
1 inch = 2,000 feet
1 inch on map =
24k inches in the real world
Most USGS topographic maps use brown contours to show the shape and elevation of
the terrain. Contour intervals vary, depending on the terrain and the scale of the map.
National Parks Digital Guide Tour (Maptech)
This grid layout has roots in
Union Peak Quadrangle,
T13N R14W , NW Section 33
7.5 Minute Series,
(Declination 19 1/2°)
John Wesley Powell
1869 Explored the Grand Canyon
1881-1884 U.S. Geological Survey Director
The People of the American West met John Wesley Powell’s expeditions across the American West; Powell insisted on an initial
survey before entry into the West (beyond the 100th meridian), which inadvertently suspended things like the Homestead Act of
1862. Photo courtesy of the Smithsonian Institution; students of Powell on 1868 expedition; painting Down the Colorado by N.
Public lands of the western U.S. were surveyed & divided into townships and
ranges, according to the U.S. Rectangular System. Similar to latitude and
longitude, townships and ranges measure a land area from north to south
(township) and east to west (range).
lies in the 2nd township south of a
particular baseline & the 3nd range
west of a particular principal
Standard township: 6 miles square Range
Township divided into 36 sections of
1 square mile each (640 acres)
Township of 36 sections, each 1 square mile (640 acres)
6 miles square
Early surveyors established section corners
The U.S. Geological and Geophysical Survey of the Territories, 1871, National Archives & Records Administration
Find the tiny red
cross/plus sign on this
It refers to a section
corner marker and the
elevation at that
Sometimes corner markers consist
of a poured concrete monument
with a brass cap; and sometimes
they consist of a wood post in a
pile of rock (e.g., areas not
surveyed since the early 20th
NW Missoula Quadrangle, Revised 1999
Also, keep an eye out for benchmarks
(references points used in surveying, with
known locations and elevations).
These are often noted on topographic maps
with a black “X.”
You should be able to locate them on the
ground by searching for a brass cap with an
(e.g., “2296” which denotes 2296 ft amsl)
Mauna Kea Benchmark, HI; CSUS Archives
How do we get more precise than a 640-acre section for our site forms?
T40N, R8W Section 7 SE ¼ of the SE ¼ of the SE (SE SE SE)
(Universal Transverse Mercator)
The earth is divided into 60 Zones. Each zone is 6° wide.
Each zone is numbered beginning at the 180° meridian near the International Date Line.
Each zone divided into 1000-meter (1 km) units.
Tick marks along the side of 7.5. minute topo maps represent 1 km within those 1000-m units
Any point in a zone can be
referenced by citing:
1. its zone number;
2. its distance in meters from
Zone 11 Zone 12
the equator (northing); and
3. its distance in meters from
a N-S reference line (easting)
in each zone; that line is the
bisecting each UTM zone.
NAD 27? NAD 83?
The North American Datum = official datum used for the primary geodetic network in
North America. In the fields of cartography and land-use there are currently two North
American Datums in use: the North American Datum of 1927 (NAD27) and the North
American Datum of 1983 (NAD83). Both are geodetic reference systems, but each is
based on different measurements.
While most USGS topographic maps use the 1927 North American Datum (NAD 27), maps
are being slowly revised to NAD 83.
Because Earth deviates significantly from a perfect
ellipsoid, the ellipsoid that best approximates its
shape varies region by region across the world. NAD
NAD 1927 is based on the 1927 best suited North America as a whole. Likewise,
Clarke Ellipsoid of 1866; it historically most regions of the world used ellipsoids
was created by manual measured locally to best suit the earth's shape those
surveying of the entire
continent. The geodetic As satellite geodesy and remote sensing technology
"center" of NAD27 is a base reached high precision and were made available
for civilian applications, it became feasible to
station at Meades Ranch acquire information referred to a single global
in Kansas. ellipsoid. This is because satellites naturally deal with
Earth as a monolithic body. Therefore the GRS 80
ellipsoid was developed for best approximating the
earth as a whole, and it became the foundation for
the North American Datum of 1983. Though
generally GRS 80 and its close relative WGS 84 are
not the best fit for any given region, a need for the
closest fit largely evaporates when a global survey is
combined with computers, databases, and software
able to compensate for local conditions…
DATUM = a fixed reference point which measurements are taken.
NAD 27 base station at Meades Ranch in
Kansas. located at 39°13′26.71218″N
/ 39.2240867167°N Geodetic = scientific discipline that deals with the measurement and
/ representation of the Earth, including its gravitational field, in a three-dimensional time-
98.5421516778 (39.224087, -98.542152,
NAD83). varying space
National Register Bulletin 28:
Using the UTM Grid System to Record Historic Sites
1. Draw a line from the top of the topo to
the bottom, connecting UTM tick marks
immediately to the west of the point.
2. Draw a line from the left to the right,
connecting UTM ticks marks immediately
to the south of the point.
3. Align the counter so that the side of the
scale that reads from right to left lies
along the east-west line and the side that
reads from left to right passes thru the
4. Read the coordinate counter scale:
right to left for easting & up for northing.
NOTE: easting values increase going east;
northing values increase going north
303 (303,000) 305
What if a site spans more than 10 acres?
Garnet Ghost Town, c. 1860s-1912 (1940s), Monte Dolack 2004
Label points clockwise starting from NE point
REDUCE extraneous area around complex site boundaries
The UTM references for Garnet are:
A 322405m E, 5187765m N;
B 321000m E, 5187771m N;
C 321702m E, 51886650m N;
D 322425m E, 5188605m N.
The legals are: E3/4 of Section 3 and the W1/4 of Section 2
There’s always GPS…
“No matter what discovery or sampling techniques are
used, the spatial location of the archaeological remains
must be RECORDED…
…discovery and geographical location are the essential
aspects of reconnaissance”
(Sharer and Ashmore 2003:242)