Components of Geographic Information

Reference Systems

Objectives of lecture:

1. Components of Geographic Information: time, space, and attribute
2. Introduce Reference Systems for Time, Space and Attribute

Basic Components/Dimensions of Geographic Information

From thematic cartography: Attribute and location two basic components of maps

Maps, as normally presented, are actually classified in terms of treatment of attributes:

• General maps: (for navigation or reference)
  • base maps (charts, non-contour component of topo maps) - recognize isolated features
• Thematic maps: (single purpose, one "theme")
  • isopleth (contour) - continuous attribute sliced at discrete intervals
  • choropleth - collection zones shaded to show classed variable
  • dasymetric- choropleth display where boundaries affected by another variable

Example: Exxon Valdez oil spill by day...

Sounds obvious. useful starting point to remember [BASIS OF THIS COURSE!]

Reference Systems

A reference system incorporates a package of decisions about measurement of some property; it provides a means to compare things (at the simplest level). [Resources]

Temporal Reference Systems

• Clocks
  The number system: Babylonian heritage (base 12 and base 60) hours, minutes, seconds [a very old technology]
  Technology of time-keeping - Network Time Protocol clocks, Universal Time, "Mean" time (average speed of earth):

  right now at UW

  more than you ever wanted to know about time from GPS sources

  Universal Time from US Naval Observatory
  Sidereal time
• Calendars
  Solar (eg. Gregorian 365 days, leap year rules, etc. based on "universal day")

  Roman origins: base dates: "ab urbs condita" (founding of Rome); 1 AD = 754 AUC (set by Dionysius Exiguus in 547 AD)
  Lunar (months, not years)
  Geological dating: 1950 established as "Present"

BASIC POINT: time is measured as a "distance", elapsed from some established starting point. A reference system implies a unit of measure and an origin along a "time line". These conventions become so accepted, they are taken for granted...

Spatial Reference Systems

• "Geographic" Latititude-Longitude
  • Based in Equator (astronomical), axis of rotation (at right angles to Equator) plus an arbitrary Zero for Longitude (Greenwich Meridian). Due to astronomical origins, time and longitude are defined basically on a common reference system.
  • (NOT absolute, but relative to a Datum, an earth model and positions for other places)
• Planar Coordinates (projections) [such as the Washington State Plane zones]

A spatial reference system includes:

These decisions are often packaged up into a conventional coordinate system (spatial reference system) such as UTM or State Plane (in the USA)

Vertical information

a special case, with extra concerns:

Space-Time

In physics (and in pulp sci-fi), it is common to refer to space and time together, since the theory of relativity makes them impossible to separate. At geographic rates of speed, these effects are hard to detect, but still it makes sense to think of a composite, using Hägerstrand's space-time diagrams.

Attribute Reference Systems

Much more complex than seven "basic" physical measurements and derived composites.

Examples abound: in the legend of any map. [limited only by your imagination!]

Population, population density, Year of maximum population, Dollars of household income per month, Vegetation type, Zoning, soil bulk density, and on and on ...

Fish and Wildlife Service "Cowardin" manual for wetland classification (and its official hierarchy)

Information content of attribute reference systems.

This is a preview of the next lecture (about levels of measurement...)

Level of measurement:	Information required
Nominal	definitions of categories
Graded membership	definition of categories plus degree of membership or distance from prototype
Ordinal	definitions of categories plus ordering
Interval	unit of measure plus zero point
Extensive ratio	unit of measure (additive rule applies)
Cyclic ratio	unit of measure plus length of cycle
Derived ratio	units of measure (ratio of units; weighting rule)
Counts	definition of objects counted
Absolute	type (probability, proportion, etc.)

The rows in grey are additions to the classical levels of measurement as taught in other geography courses....