Accuracy & Visualization...Database Creation Process Adapted from P.A. Burroutgh, 1986,...

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