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presented by:Tim Haithcoat
University of MissouriColumbia
Accuracy&
Visualization
Database Creation ProcessDatabase Creation ProcessAdapted from P.A. Burroutgh, 1986, Principles of Geographical Information Systemsfor Land Resource Assessment, Oxford, Fig. 4.7, p. 66
Data Collection
AttributesLinked by
Unique IdentifiersSpatial Data
Registration
Rectification
Digitize
Scan
Convert to Vector
Build Topology
Visual Check
Edit
Add Identifiers Manually
Input toText File
Link AttributesTo Spatial Data
GIS DATABASE
The Inherent Properties Of Na tu re:
- gradual- fuzzy
The Na tu re of M ea su rem ent:
- capabilities instruments- capability of observer- scale & frequency of
observations
LIK ELY ERROR IN G IS DAT A
The M odels Used to Com m u nica te
M ea su rem ents:- entity structure
- generalization/aggregation of results
Medium of communication
T ools Ava ila ble for Ana lysis:
- GIS- supplementary data
Appropria te M ethods for Dea ling w ith
Error in Deriva tive Prod u cts
Pu rpose of the User:- scope & scale- impact of error
Composite Map Accuracy for the OR Operator
00.10.20.30.40.50.60.70.80.9
1
1 2 3 4 5 6 7 8 9 10
Number of Data Layers
Com
posi
te m
ap a
ccur
acy
Composite Map Accuracy for the AND Operator
00.10.20.30.40.50.60.70.80.9
1
1 2 3 4 5 6 7 8 9 10
Number of Data Layers
Com
posi
te m
ap a
ccur
acy
Maps of soil & forest cover can
be linked to their relative uncertainty.
Lighter tones indicate less
certain areas around spatial
transitions.
soil
fore
st c
over
The coincidence of the soil & forest
maps can be linked to their joint
uncertainty. Lighter tones indicate less
certain areas around the
coincidence of feature boundaries.
soil
fore
st c
over
Slivers: the classic form of overlay error
A sim ple illu stra tion: 2 ca teg ories
(A,B) 2 sou rces
(u pper/low er)
Aaa
bA
B Bb
Another case of overlay error
AB
Ba
Aa
Transitional intermediaries between pure position error and attribute error
not clea r tha t fea tu res a re
intended to be the sa m e
tra nsitiona l interm edia ries betw een pu re position error &
a ttribu te error(for exa m ple)
1/4 of lines from one
sou rce, 3/4 from the other
Scale adds a dimension to the transition(note: previous diagram now the diagonal)
sca lesa m e
onesou rcem ore
deta iledattribute filter
attribute error
intermediate
sliver
positional error
scal
e ax
is
• The precision of GIS processing is effectively infinite.
• All spatial data are of limited accuracy.• The precision of GIS processing exceed the
accuracy of the data.• In conventional map analysis, precision is usually
adapted to accuracy.• The ability to change scale and combine data from
various sources and scales in a GIS means that precision is usually not adapted to accuracy.
• We have no adequate means to describe the accuracy of complex spatial objects.
• The objective should be a measure of uncertainty on every GIS product.
Error Source Identification
Strategies for Error Reduction
Strategies for Error Management
Error Propagation Modeling
Error Detection and Measurement
Hierarchy of NeedsThe attachment of successively higher-order needs is dependent on the satisfaction of the needs at the lower levels .
Error Source Identification
• Basic problem of identifying and classifying sources of error
• Two sets of basic distinctions:• Cartographic error: positional, locational• Thematic error: attribute, descriptive
• Measurement: imprecision in the assigned ____, digitizing
• Conceptual, real world: map objects, generalization
Error Source Identification
Strategies for Error ReductionStrategies for
Error ManagementError Propagation Modeling
Error Detection and Measurement
Error Detection & Measurement
• Methods of assessing accuracy levels in spatial data
• Thematic error– Confusion matrix– Appropriate for _____ data– Numeric data?
Error Source Identification
Strategies for Error ReductionStrategies for
Error ManagementError Propagation Modeling
Error Detection and Measurement
Error Propagation Modeling
• Concerned with the consequences of applying GIS operations to spatial data
• Two phases– Propagation: errors present in data are passed
through & accumulate in output– Production: errors in output are mainly
attributable to the operation itself
Error Source Identification
Strategies for Error ReductionStrategies for
Error ManagementError Propagation Modeling
Error Detection and Measurement
Strategies for Error Management
• Meta needs• Go beyond error assessment ____ and ___
concerns with inferences that may be drawn from the results– Examples:
• Coping with errors in output ______• Methods for decision-making in the presence of
error• Minimum standards for acceptance
Error Source Identification
Strategies for Error ReductionStrategies for
Error ManagementError Propagation Modeling
Error Detection and Measurement
Strategies forError Reduction
• Tim, anything to add?
Error Source Identification
Strategies for Error ReductionStrategies for
Error ManagementError Propagation Modeling
Error Detection and Measurement