How to discern measurement frameworks

(courtesy of Chrisman)

Objectives of this exercise:

  1. Participate in a discussion session in class.
  2. Examples of maps and their underlying measurement framework
  3. Introduce data sources to be used in exercises
  4. Each group (of size 3 or so) will be given on source to report on:
  5. Measurement scale (level)
  6. Reference systems (spatial, temporal, attribute)
  7. Measurement framework
  8. Representation

Purpose

The steps from measurement to representation involve a number of decisions that influence the potential use of geographic information. Data sources start with raw measurements, and place them in context so that they can be interpreted as information. Specifically, all geographic information is placed in a temporal reference system, a spatial reference system, and an attribute reference system. But the reference system is not enough to determine what you can do with a source of information. The concept of a measurement framework encapsulates the selection of components that act as 'control' so that another component can be measured. Finally, information is represented in database and on a map using systems of symbols. In reading a map we need to peel back these layers to figure out what happened in the whole process.

In this exercise we ask you to work in groups of three or four to discuss and evaluate geographic data.  Each group member should be prepared to answer questions about levels of measurement, reference systems for time, space and attribute, measurement frameworks (what is controlled, fixed,  measured regarding time, space and attribute?) and representation (is it vector or raster?) for one of the four groupings of data.  Please use Chrisman chapter 2 as a reference text.

  1. level of measurement (and specific scale of measurement)  note: ignore references to "pop quiz" etc ;-)
  2. use of reference systems for time, space and attribute
  3. measurement framework (using the typology in Chrisman Chapter 2).   (see hand out reading)
  4. representation (how the measurements are transformed and presented)

Issues to consider

Methods of presenting geographic information have become somewhat ritualized through the influence of disciplinary training and bureaucratic traditions. Consider whether the product you describe was designed for a specific purpose or for a more nebulous 'general purpose' constellation of users.

Printed maps impose a number of constraints on the display of information. The size of the printing press, the colors available, the density of symbols all create a style of presentation that continues to influence the digital products. Many of these products started out as printed maps, so that approach still influences the digital database.

What to do

  1. Examine your material: (using ArcMap and various source descriptions- metadata).
  2. Prepare materials for presentation. Cover the following points:
  3. Measurement scale (and level)
  4. Reference systems used
  5. Measurement framework (what is controlled/measured? How?)
  6. Representation (How was the picture/database constructed? How do these steps alter the underlying information?)
    7.
  7. Your group presents their results in discussion meeting

Resources for this exercise

The Bainbridge Island data can be accessed by opening P:\cp200\workshop\discussions\d1.mxd.  Each group will examine one of the source data layers. Each group has TWO layers. Try to draw a comparison/contrast between your pair.

  1. Land Cover classified from Landsat 1998 & Streets
  2. Land Cover (vegetation) from airphotointerpretation 1971 & Forest Practices Act
  3. Schools & Normalized Vegetation Difference Index (NDVI)
  4. soils  (specifically K factor) & 10 meter DEM from USGS

Some Hints on how to discern a measurement framework

But also, peel back the representation

Version of 18 October 2006