Representation and Management of Spatial Error in Cadastral Databases Dr. Panos Lolonis Manager of the Planning, Research and Development Division Coordinator.

Representation and Management of Spatial Error in Cadastral Databases

Dr. Panos Lolonis

Manager of the Planning, Research and Development Division

Coordinator of the Planning and Quality Department

Ktimatologio S.A. (Hellenic Cadastre S.A.)Ktimatologio S.A. (Hellenic Cadastre S.A.)

Mesogion 288Mesogion 288

GR-GR-15562, 15562, Holargos-AthensHolargos-Athens

Tel.: +30-1-6505-829Tel.: +30-1-6505-829E-mail: [email protected]

OutlineOutline

Conventional approach for handling spatial Conventional approach for handling spatial cadastral datacadastral data

Shortcomings of the traditional approachShortcomings of the traditional approachRepresentation of spatial cadastral data and Representation of spatial cadastral data and

their accuracytheir accuracyManagement of data and their accuracyManagement of data and their accuracyUse of stochastic spatial data in land management activitiesUse of stochastic spatial data in land management activitiesConclusionsConclusions

Conventional Approach for Handling Spatial Cadastral Data

Conventional Approach for Handling Spatial Cadastral Data

Lack of accuracy about the locations of cadastral dataLack of accuracy about the locations of cadastral data   Use of data in deterministic fashionUse of data in deterministic fashion

Consequences and shortcomingsConsequences and shortcomings Lack of specificity about the level of accuracy Lack of specificity about the level of accuracy

(“more or less”)(“more or less”) Inconsistencies among different series of Inconsistencies among different series of

measurementsmeasurements Inconsistencies among values of documentsInconsistencies among values of documents Problems in the use of cadastral data in applicationsProblems in the use of cadastral data in applications

(zoning regulations, tax agencies)(zoning regulations, tax agencies)

Importance of accurate locational cadastral data

Extract from a ContractDefinition of the size and dimensions of

the parcel

Extract from a ContractDefinition of the size and dimensions of

the parcel

Cadastral Map Land parcels in a city block

Cadastral Map Land parcels in a city block

Cadastral Extract of a Land Parcel Cadastral Extract of a Land Parcel

Cadastral Extract Sent to Owners Cadastral Extract Sent to Owners

Differences between Declared and Computed Areas

Differences between Declared and Computed Areas

0

10

20

30

40

50

60

< (-

50)

(-50

) -

(-20

)

(-20

) -

(-10

)

(-10

) -

(-5)

(-5)

- (

-2)

(-2)

- (

2)

(2)

- (5

)

(5)

- (1

0)

(10)

- (

20)

(20)

- (

50)

> (5

0)

Category

Per

cen

t (%

)

Urban

Rural

A’ Pilot ProgramThe Hellenic Cadastre Project

Municipalities:Urban: Chalandri

Rural: Megas Alexandros

Public Opinion about the Benefits of the Hellenic Cadastre

Public Opinion about the Benefits of the Hellenic Cadastre

Category

• Settlement of the boundaries of the properties of individuals

• Protection from land infringement• Determination of public land• Facilitation of land transactions• Protection of forests• No benefits• No answer

Sample size: 1495Date: December 1999

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7

Category

Perce

nt of

resp

onse

s (%)

Representation of Spatial Cadastral Data and Their Accuracy

Representation of Spatial Cadastral Data and Their Accuracy

Tag standard errors and covariances to the coordinate Tag standard errors and covariances to the coordinate datadata

Computation of derivative variables and their accuracyComputation of derivative variables and their accuracyLengthsLengthsAreasAreasAnglesAngles(Use of the Error Propagation Law)(Use of the Error Propagation Law)

Need to incorporate functions into computer-based Need to incorporate functions into computer-based cadastral systems to handle errorcadastral systems to handle error

Locational Accuracy of Points, Sides and Areas

of Land Parcels

Locational Accuracy of Points, Sides and Areas

of Land Parcels

Area = 1854.84 m2(1834.64 – 1875.03)

Management of Data and their Accuracy

Management of Data and their Accuracy

Adoption of the stochastic frameworkAdoption of the stochastic frameworkprovides new flexible ways to deal with problems provides new flexible ways to deal with problems

and proceduresand procedures requires a different approach to carry-out land requires a different approach to carry-out land

administration tasksadministration tasks

Procedures for updating dataProcedures for updating dataTesting about the coincidence of old and new Testing about the coincidence of old and new

datadataAmalgamate old and new informationAmalgamate old and new information

Use of Stochastic Spatial Data in Land Management Activities

Use of Stochastic Spatial Data in Land Management Activities

Compilation of legal documents (contracts)Compilation of legal documents (contracts) Incorporate expected values, confidence intervals and Incorporate expected values, confidence intervals and

confidence levels into documents and diagramsconfidence levels into documents and diagrams

Satisfying zoning regulations (Test hypotheses)Satisfying zoning regulations (Test hypotheses)::AreasAreas

HHoo: Area >= 400 m: Area >= 400 m22 H H11: Area < 400 m: Area < 400 m22 at the 95% at the 95% confidence levelconfidence level

LengthsLengthsHHoo: Length >= 15 m: Length >= 15 m H H11: Length < 15 m: Length < 15 m at the 95% at the 95% confidence levelconfidence level

Resolving boundary disputesResolving boundary disputes

Need to reform legislation to incorporate the stochastic Need to reform legislation to incorporate the stochastic notions (expected values, standards errors, confidence levels)notions (expected values, standards errors, confidence levels)

Conclusions Conclusions

Accuracy information must be explicitly incorporated and Accuracy information must be explicitly incorporated and handled into cadastral databaseshandled into cadastral databases

Cadastral data that incorporate accuracy measures are Cadastral data that incorporate accuracy measures are more informative and more useful in land management more informative and more useful in land management activitiesactivities

There is a need to promote development of:There is a need to promote development of: GIS software that can handle probabilistic dataGIS software that can handle probabilistic data Legislation that is in conformance with probabilistic Legislation that is in conformance with probabilistic

reasoningreasoning

Goal: To develop cadastral systems that combine data Goal: To develop cadastral systems that combine data about location, accuracy and time in a tightly integrated about location, accuracy and time in a tightly integrated framework.framework.