Supporting Resources
Index of Resources:
Some definitions
[extracted from on-line Glossary
for Exploring GIS]
- Measurement framework A scheme that establishes rules
for control of other components of a phenomenon that permit the
measurement of one component. In a geographic information system,
there are three components: time, space, and attribute.
- Control A mechanism of restraint on the variation
of a system to permit measurement of one component of a phenomenon
while other components only vary within the limits of the control.
- Isolated object frameworks a general term covering
those measurement frameworks that use a specific attribute value
as a control to obtain spatial measurements; includes spatial
object and isoline frameworks.
- Spatial object framework a measurement framework that
identifies a particular category, then maps the location of that
object (as a point, a line or an area).
- Feature cartographic feature: an instance of a defined
class of objects that cannot be divided into objects of the same
type.
- Contour / isoline contour line: a line connecting
points of equal elevation on a topographic surface. An isoline
generalizes this concept for any continuous distribution.
- Isoline framework a measurement framework that establishes
control by a systematic set of slices through an attribute to
obtain lines that represent the surface.
- Connected coverage frameworks a general terms for
measurement frameworks that involve relationships between distinct
spatial objects; includes network and categorical coverage frameworks.
- network framework a measurement framework based on
a set of distinct spatial objects (usually instances of linear
objects like roads or rivers) that connect to form a network.
- categorical coverage an exhaustive partitioning of
a two-dimensional region into arbitrarily shaped zones that are
defined by membership in a particular category of a classification
system.
- DEM a framework for recording spot elevations in a
regular rectangular grid (matrix); an acronym originally created
from Digital Elevation Model at US Geological Survey. To avoid
ambiguity, DEM will be used exclusively for a grid framework,
so it can be read matrix.
- Indirect measurement a procedure that assigns attributes
to spatial objects through some attribute of those spatial objects
(such as a soil class or a political subdivision), not through
direct measurement.
- Choropleth framework measurement framework whose spatial
units (derived from a categorical coverage of named objects)
serve as control for attribute measurement (e.g. census tabulation)
- Choropleth map A thematic mapping technique that displays
a quantitative attribute using ordinal classes applied as uniform
symbolism over a whole areal feature. Sometimes extended to include
any thematic map based on symbolism applied to areal objects.
Some more definitions of broader concepts surrounding measurement
frameworks
- Data model In the database literature, general description
of sets of entities and the relationships between these sets
of entities (Ullman 1982); collection of object types, collection
of operators on those object types and a collection of integrity
constraints (Codd 1981). In a GIS, composed of a measurement
framework and a scheme for representation
- Database Structured collection of data with software
to provide access in different ways; has a data model, a data
structure and an implementation (representation)
- Geodetic control a set of surveyed monuments used
to define a spatial reference system for a particular project.
[source of confusion with "Control"]
- Resolution least detectable difference in a measurement;
in a geographic context, resolution applies to all components
(time, space and attribute) according to the measurement framework.
Not identical to accuracy.
- Accuracy closeness of a measurement to a value thought
to be true; repeatability can be estimated by repeated measurement,
measured by variance for continuous measures; accuracy of classification
for categories can be summarized by a misclassification matrix
when compared to a survey of greater accuracy.
- Primitives basic components that are sufficient to
build a larger system; the primitives of two-dimensional geometry
are points, lines, and areas.
Some Examples of data sources that illustrate measurement
framework choices
Bainbridge Island data sets
Index of Bainbridge Island
data
Examples of Willapa Bay data sets
Index of Willapa Metadata
(all layers)
More Examples
Data Descriptions: Global Data
From the Global Land Information System and United Nations
GRID project site at cozy Sioux Falls, South Dakota (now disappeared
from the web, sad to say):
For example: World coverage of raster representations used for
climate models.
Predominant type: Vegetation: one degree cells (NOT
SQUARE!) classed into 32 types
Percent cover: Intensity of Cultivation: five land
classes of percent cultivated 0,20,50,75,100; plus water
Sum: Annual rate of methane production (mostly from
cows)...
Albedo (reflectance): assigned to vegetation classes by Indirect
measurement...
Predominant type: 38 zones in half-degree cells: two
scenarios
Normal (current conditions)
Scenario based on doubling of atmospheric carbon dioxide
(greenhouse gas)
Global soil texture data
Percent cover: 33 files of percent cover for 27 (3 depths
X 3 textures X 3 slopes) plus non-soil classes
ISOLATED object framework (at least partially)
five files describing methane characteristics of wetlands
plus a "fractional inundation" measure (percent of
cell covered by wetlands)
World Soil Data
These two show how an attribute-controlled source can be converted
(transformed) into a cellular representation. There isn't a good
set of common terminology to flag this MAJOR conversion.
From here: Back to Lecture 05
| Class Resources | Lectures
| Exercises and Discussions | How to contact us
Version of 08 October 2003