georeferencing and spatial mapping Flashcards
spatial referencing systems
georeferencing: principles and process of transforming spatial data from an arbitrary system into a geographic or projected system
- aka: registration, coregistration, geometric transformation
ellipsoid
when sphere parameters (a) is not equal to (b) - accounts for shape and buldge and earths rotation
name some official ellipsoids
WGS84
Australian
Everest
why are there so many ellipsoids
existed before satellite technology - each country used the North American Datum 1927 (NAD27)
geoid
accurately represents the earths shape and size
based on equipotential gravity surfaces at mean sea level
rock densities cause the geoid to deviate from the ellipsoid
Datum
measurements taken on the earths surface
raw measurements “levelled” to a geoid
draw geographic coordinate systems
slide 10
projected coordinate systems
Involves determining the locations of features on the Erths curved surface and then transforming these location info positions on a flat map
2 issues involved in PCS
what type of curved surface is the earth
how to represent the curved surface of the earth in a plane
representing the curved surface of the earth on a flat surface
- when the surface is PLANE (azimuthal projections)
- when the surface is CYLINDER (cylindrical projections)
- when the surface is CONE (conic projections)
how do map projections distort the earth?
- accurate transformation of ANGLES (conformal or orthomorphic projections)
- accurate transformation of AREAS (equal-area or equivalent projections)
- accurate transformations of DISTANCES (equdistant projections)
- accurate transformation of DIRECTIONS (azimuthal and gnomonic projections)
UTM system
- UTM is a world-wide system defined in meters
the world is divided into 60 zones, 6 degrees of longitude each, from 84N - 80S latitude
each zone divided by a central meridian and equator
lat/long to decimal degrees
slide 17
cartography (fisher)
involved with the graphic communication of spatial relationships and distributions and includes the analysis and manipulation of geographic data to enhance representation
cartography (intl catographic assn)
art, science, and technology of producing, using and studying maps
maps
primary output of GIS analysis
scaled representation or model of geographic reality portrayed using a selected set of features on a flat medium
map scale
defines the ration b.w distance on a map and corresponding distance on ground
fractional scale
numerical expression
verbal scale
written
graphic scale
calibrated bar or line
generalization
process of choosing which features to represent on the map and how they will be represented
classification
simplification
exaggeration
symbolization
induction
classification
expressing the key characteristics of a distribution
simplification
determining important characteristics if feature attributes and elimination of non-important ones
exaggeration
enlarging or altering the features in order to capture the real-world importance
symbolization
assigning graphic marks on the maps to features from the real world
induction
making inferences on relationships among features on the map
map design hierachy
target audience
map components
arranging features
= spatial data
types of spatial maps
simple choropleth maps: used to visualize tabular statistics geogrpahically and compare magnitudes in various places
classless choropleth map: ration-scale portrayal of the attribute value and represent a clear pic of the existing complexity of the geographic space
procedure for creating choroplethic maps depnds on
size and shape of unit areas
number of classes (6 or 7)
class limit determination
components of a good map
map title
legend
north arrow
scale
labels and text
