Location and Technology

GRID REFERENCE SYSTEMS

Grid reference systems greatly accelerate the use of an atlas to locate unfamiliar places. There are several different types, but latitude and longitude (based on the Earth's spheroid geometry, and tied to internationally standardized "starting points") comprises the most common one. See page 18 in your textbook for more about the derivation of this system. We will use it.

EXPRESSION OF ARC DISTANCES

Arc arithmetic is based on the concept that there are 360 degrees in a circle (or along a plane through a sphere); one degree (1^o) can be divided equally into sixty minutes (60'); each minute is divisible into sixty seconds (60"). Thus, 51^o-25'-42.9" means a curved line that is 1/7 of a full circle.

EXPRESSING LOCATION ON A SPHERICAL EARTH

Latitude 0^o is the Equator (the maximum surface circumference around which the Earth rotates), and latitude increases by arc units in both the northern (N) and southern (S) hemispheres up to 90^o-00'-00" at each Pole. Latitude lines never cross, so they are sometimes called parallels; the distance across each 1^o of latitude is ~69 statute miles.

Longitude 0^o is a line running from pole to pole that passes through Greenwich, England. Longitude increases by arc units in both the eastern (E) and western (W) hemispheres up to 180^o-00'-00". Longitude lines (sometimes called meridians) converge at the poles, so distance between each 1^o of longitude diminishes as one travels poleward; distance is NOT consistent!.

I specify location coordinates in this course by a latitude and a longitude value (in arc units), and the hemisphere; e.g., Stevens Point is at 44^o-30'N/089^o-35'W. Usually in this course you will only need to pinpoint sites to the nearest 1/2^o (meaning, the nearest 30') of latitude or longitude.

See also the page discussion our GPS receivers.

N. C. Heywood maintains this page, last updated 10NOV99.