Spatial Reference Systems

Objectives of lecture

• first in series on geometric component of geographic information
• identify the tickmarks around maps and how to use them...

How do we locate ourselves (and other things?)

• Places and place names (here, there)
• Itineraries (sequences of places and paths)
• Relative (left, right, up, down, near, far)
• Absolute (external frame of reference, relationships- distance, direction- GEOMETRY)

Place Names

Place as named "thing"

Historical sideshow: cultural overlays on the landscape

• Imperialist expansion: rapid naming, evoke sponsors of expedition, places back home, etc.(eg. Mt. Rainier, Puget Sound, Columbia, Astoria etc.)
• Settler names: feeling of solidity, prosperity, evoke political events and heros (eg. Bainbridge Island, Everett, Bellevue, Olympia)
• Aboriginal names: often mislocated, distinct classes of features (rivers, more than towns...) (eg. Whatcom, Skagit, Snohomish, Stilliguamish, Snoqualmie, Tahoma (Tacoma), Seal'th (Seattle))

Places: not ordered, have to know where they are (so what kind of reference system can they provide to an outsider?)

Street signs: are they there to make the map correct? (part of a map-ground correspondence technology)

The REAL spatial reference framework:

Geographical Coordinates (latitude / longitude)

based on some clear choices and some arbitrary ones

Polar axis of rotation: Establishes NORTH, Equator as plane at right angles

Latitude is ANGLE from Equator (North or South) (Parallels)

This was the easy part: shadow of stick at noon, Polaris at night...

Longitude: angle around Earth (Meridians), has to be measured from an arbitrary Zero (prime meridian)

Why Greenwich? (British made the bulk of nautical charts)

Notation: Bablylonian base 60: 127° 15' 00" = 122.2500 (decimal degrees)

These are ANGLES, distances vary northward (latitude vanishing to zero at poles)

Shape of the Earth? Topic considered later, latitude/longitude is basically spherical...

Planar Coordinates

X,Y coordinates in distance units; attempt to flatten the Earth [see PROJECTION lecture next Monday]

Local: archaeological digs (grid of string); ecological study sites (grid of pipes)

What you see on maps (as ticks around topographic quads)

State Plane Coordinates

125 zones across USA

Washington (and Oregon) have two zones ("North" and "South" for each state) Lambert Conformal Conic projection [see projections, of course]

Idaho has three Transverse Mercator zones (in North/South bands called East, Central, and West)

Distance on OLD version in feet (now meant to be in meters)

Universal Transverse Mercator

uses a methodical 6° band of longitude for each zone, coordinates always in meters

connects in military mapping to the Military Grid (a way to turn coordinates into a letter code)

16TCC0571 = 4771000 N, 305000 E

Computer Graphics are based on coordinates, but GPS (next lecture) may make latitude longitude the system of choice. The old reasons of simple calculation may not matter...

Muehrcke covers Public Land Survey and Land Records (hold these for later)

Public Land Survey System (Township and Range)

appears to be like a coordinate system, too many peculiarities to be treated mathematically.

Version of 25 January 2000