| A | B | C | D | E | F | G |

| H | I | J | K | L | M | N |

| O | P | Q | R | S | T | U |

| V | W | X | Y | Z |

TTT

talus - Rock debris at the base of a mountain or cliff.

tank - A usually artificial pool, pond, reservoir, or cistern, especiallly one used to hold water for drinking or for irrigation.

tarn - A small mountain lake, especially one formed by glaciers.

theodolite - An optical instrument consisting of a small mounted telescope rotatable in horizontal and vertical planes, used to measure angles in surveying, meteorology, and navigation.

TIGER - Topologically Integrated Geographic Encoding & Referencing - A U.S. Census Bureau mapping system.

time to first fix - See TTFF.

TOPEX - TOPography EXperiment for Ocean Circulation; unflown NASA precursor mission to TOPEX/Poseidon.

topography - The graphic representation of the landform on a map by the use of contour lines.

township - A unit of survey of the public lands of the United States, normally a quadrangle approximately 6 miles on a side with boundaries conforming to meridians and parallels within established limits, containing 36 sections.

track - A collection of points that show the path travelled.

track point - A single point on the path travelled.

transit - A precision surveying instrument; a theodolite in which the telescope can be reversed in direction by rotation about its horizontal axis.

triangulation - The method of determining a location on a map by using two or more points through which lines of known directions are drawn; the intersection of these lines is the desired location; can use distance and/or angles.

trilateration - The same method as triangulation, except trilateration uses only distances for locating.

troposphere - The portion of the atmosphere from the earth's surface to the stratosphere.

true north - The geographical north pole.

TTFF - Time To First Fix - The time it takes for a GPS receiver to lock onto the satellite signals and determine the initial position.