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.)
Mesogion 288
GR-15562, Holargos-Athens
Tel.: +30-1-6505-829
E-mail: plolonis@ktimatologio.gr
Outline
 Conventional
approach for handling spatial cadastral
data
 Shortcomings of the traditional approach
 Representation of spatial cadastral data and their
accuracy
 Management of data and their accuracy
 Use of stochastic spatial data in land management activities
 Conclusions
Conventional Approach for Handling
Spatial Cadastral Data

Lack of accuracy about the locations of cadastral data

Use of data in deterministic fashion

Consequences and shortcomings
 Lack of specificity about the level of accuracy (“more
or less”)
 Inconsistencies
among
different
series
of
measurements
 Inconsistencies among values of documents
 Problems in the use of cadastral data in applications
(zoning regulations, tax agencies)

Importance of accurate locational cadastral data
Extract from a Contract
Definition of the size and dimensions of the
parcel
Cadastral Map
Land parcels in a city block
Cadastral Extract of a Land Parcel
Cadastral Extract Sent to Owners
Differences between Declared and
Computed Areas
60
A’ Pilot Program
The Hellenic Cadastre Project
40
Urban
30
Municipalities:
Urban: Chalandri
Rural
20
Rural: Megas Alexandros
10
Category
> (50)
(20) - (50)
(10) - (20)
(5) - (10)
(2) - (5)
(-2) - (2)
(-5) - (-2)
(-10) - (-5)
(-20) - (-10)
(-50) - (-20)
0
< (-50)
Percent (%)
50
Public Opinion about the Benefits
of the Hellenic Cadastre
Category
70
•
Percent of responses (%)
60
50
•
•
•
•
•
•
40
30
20
10
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
0
1
2
3
4
Category
5
6
7
Sample size: 1495
Date: December 1999
Representation of Spatial Cadastral
Data and Their Accuracy

Tag standard errors and covariances to the coordinate data

Computation of derivative variables and their accuracy
 Lengths
 Areas
 Angles
(Use of the Error Propagation Law)

Need to incorporate functions into computer-based cadastral
systems to handle error
Locational Accuracy of Points, Sides and
Areas
of Land Parcels
Area = 1854.84 m2
(1834.64 – 1875.03)
Management of Data and their Accuracy

Adoption of the stochastic framework
 provides new flexible ways to deal with problems and
procedures
 requires a different approach to carry-out land
administration tasks

Procedures for updating data
 Testing about the coincidence of old and new data
 Amalgamate old and new information
Use of Stochastic Spatial Data in Land
Management Activities

Compilation of legal documents (contracts)
 Incorporate expected values, confidence intervals and
confidence levels into documents and diagrams

Satisfying zoning regulations (Test hypotheses)
 :Areas
Ho: Area >= 400 m2
H1: Area < 400 m2
the 95% confidence level

Lengths
Ho: Length >= 15 m
the 95% confidence level
H1: Length < 15 m
at
at

Resolving boundary disputes

Need to reform legislation to incorporate the stochastic
notions (expected values, standards errors, confidence levels)
Conclusions

Accuracy information must be explicitly incorporated
and handled into cadastral databases

Cadastral data that incorporate accuracy measures are
more informative and more useful in land management
activities

There is a need to promote development of:
 GIS software that can handle probabilistic data
 Legislation that is in conformance with probabilistic
reasoning

Goal: To develop cadastral systems that combine data
about location, accuracy and time in a tightly integrated
framework.