Cadastral Data Modelling Digital Cadastral Databases

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Cadastral Data ModellingDigital Cadastral
Databases

• Mohsen Kalantari
• Land Administration - 2006

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Presentation Overview

• What is data modeling?
• Importance of data modeling
• Data modeling for data capture
• Isolated vs Coordinated (Integrated) Surveys
• Data modeling for database design
• Digital Cadastral Databases (DCDBs)
• Data modeling for cataloging purposes
• What is recorded in a DCDB?
• Data modeling for exchange of DCDBs
• Exchange language for maintenance of the DCDB
• Victorian DCDB
• Other DCDB examples
• Key Concepts

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What is data modeling?

• The database is specified by a data model
  describing what sort of data will be held, and
  how it will be organized.

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What is data modeling?

• Data Modeling is a Design activity like
  architecture. Do not expect to find a single
  correct answer.
• The requirement of data modeling process are
  flexible enough to accommodate a variety of
  different solutions, try to be Creative, then you
  will always have Choices.
• Data modeling is NOT data analysis, the
  difference is like prescription versus
  description.

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Why is the data model so Important?

• A small change to the data model may have a major
  impact on the system
• Example Spatial and non-spatial identifiers
• The program design heavily depends on data
  modeling
• Example Network analysis needs topology
• A well designed data model can make programming
  simpler and cheaper
• Example Automatic adjustment of parcel
  boundaries facilitates calculation of a parcel
  area
• Poor data organization is often expensive to fix
• Automatic accuracy check
• A very powerful tool for expressing and
  communicating business requirements. It can take
  us more directly to the heart of the business
  requirements.

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Evaluation Criteria

• Completeness
• Non-redundancy
• Enforcement of Business Rules
• Data Reusability
• Stable and Flexible
• Simplicity
• Communication Effectiveness

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Data Modeling Approaches

• Function Driven
• Focuses on function specification
• Example e-conveyancing , digital signature,
  financial settlement
• Data Driven
• Emphases on developing data model before detailed
  function
• Example digital cadastral database
• Prototyping
• Cut and try approach dont waste the time build
  , show, modify, show it again

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Cadastral Data Model

• A cadastral data model describes what sort of
  data will be held, how it will be organized in a
  cadastral system.

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Data Modeling and Data Capture

• Isolated Survey Approach
• Isolated parcel surveys, connected but not fully
  integrated to neighboring parcels
• Graphical Accuracy only
• Usually a mix of survey accuracy to map accuracy
  as a result of digitisation of original base maps
• Most common form of cadastre across Australian
  States and Territories (with exception ACT)

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Data Modeling and Data Capture

• Isolated survey data model

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Data Modeling and Data Capture

• Coordinated Survey Approach
• Integrated parcel surveys support a coordinated
  cadastre
• Survey accuracy, where a parcel survey
  incorporates surrounding parcels and are fully
  tied into each other
• a Survey Accurate DCDB is based on coordinates
  determined by ground surveys which are used to
  define, describe and re-define parcel boundaries.
  For all practical purposes, the coordinates in
  this DCDB are the true coordinates result is a
  fully coordinated survey system

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Data Modeling and Data Capture
Coordinated survey data model
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Graphical vs. Survey Accurate Cadastre

• Level of accuracy is usually survey accuracy
• Isolated Survey Approach leads to a non-survey
  accurate DCDB
• Coordinated Survey Approach leads to a survey
  accurate DCDB which in turn supports a
  coordinated cadastre
• What are the Advantages and Disadvantages of
  non-survey accurate DCDB?
• What are the Advantages and Disadvantages of a
  survey accurate DCDB?

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Graphical vs. Survey Accurate Cadastre

• Non-Survey Accurate (Graphical) DCDB
• Common approach in Australia
• Less required to setup/maintain DCDB
• More time to complete surveys (less connection to
  neighbouring parcels) but need to re-establish
  parcel nearly every time and connect to geodetic
  control
• Inappropriate use of non-accurate cadastral
  dataset
• Survey Accurate DCDB
• More required to setup/maintain DCDB (up to
  Billions)
• More time to perform initial survey, however very
  little work required to re-do same parcel
• Value-added potential of accurate cadastral
  dataset

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Data Modelling and Cadastral Databases

• Representation of the geometric component of a
  cadastre in electronic format is termed Digital
  Cadastral Database (DCDB)

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Data Modelling and Cadastral Databases
The physical designer sometimes is not able to
meet performance requirements, so logical
database design is not direct equivalent of the
data model
Selected Relations between Data
Logical Database Design
Program
data
Data Model
Physical Database Design
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Data Modelling and Cadastral Databases

• The performance of the information system is
  primarily the responsibility of physical
  designer
• But the alternative to improve the performance
  might be to modify the data model

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Data Modelling and Data Catalogue

• Consists
• Parcel boundaries
• Easements
• Other Additional Contents
• Property boundaries
• Building footprints
• Street addresses
• Administrative boundaries
• Valuation
• Other land use features (garden, roads, railway
  lines, forest, etc.)

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Data Modeling and Data Exchange
Data model in UML
Data model in exchange format
Convert
Switzerland cadastral data model - Interlis
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Data Modeling and Data Exchange
Step 1 Selecting parcels
Step 3 Validation and locking. Step 4
Making new state active after decision
Export to XML
Step 2 Import from XML
surveying company
Modify
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Updating of DCDBs

• Subdivisions are charted in LTO's (Land Registry)
  on an index map
• Update of the DCDB refers to those processes
  that ensure that all new and existing legal
  subdivisions are recorded, ie. the cadastral map
  or DCDB is up-to-date
• Specifically this should include
• Recording all new legal subdivisions
• Ensuring map completeness

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Upgrading of DCDBs

• Upgrade activities (an improvement, not
  maintenance)
• increase accuracy
• inclusion of survey measurements
• alignment of cadastral features with topographic
  features
• changes in data model
• generation of topological structures
• inclusion of historical layer
• unique identifiers for spatial entities

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Historical Perspective of Australian
State/Territory DCDBs

• Digistised from best available paper maps
• Urban, Rural and Metro
• varying accuracy
• /- 0.5m - 2m in Urban Metro areas
• /- 20m or more in Rural areas
• sourced from different bodies
• different data emphasis

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Observations of Australian State/Territory Data
Model

• Australia wide cadastral coverage, varying
  accuracy
• Data models are mostly based on graphical
  cadastre
• Data models High GIS focus
• Individual State and Territory solutions
• Meta data
• Incremental updates
• Accuracy upgrade (graphical to survey)
• Incremental Update

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Victorian DCDB VicMap Property

• Combination of digitised paper maps and datasets
  held by Water authorities (MMBW)
• Vicmap Property, previously known as the State
  Digital Cadastral Map Base
• Isolated Survey system, non-survey accurate DCDB
• Higher accuracy in Urban and Metro regions, lower
  accuracy in regional areas
• Very good cadastral coverage, over 90 of
  property recorded
• Geodetic datum AMG GDA94, not yet fully adopted

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Institutional Issues

• Land Victoria has responsibility for the Cadastre
  
• Land Titles Offices (Land Registry)
• Registrar of Titles
• Freehold and Crown land registration
• Surveyor-General
• Surveying/Cadastral standards
• Crown lands acquisition, alienation,
  identification
• Regulation of Surveyors
• Valuer-General
• Property Valuation
• Valuation responsibility of Local Government
• Mapping Agencies (Land Information Group)
• Maintenance of DCDB and other key datasets
  (VicMap)

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Victorian DCDB Organisations Involved in
Updating
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Key Concepts

• Data modelling approaches
• Cadastral Data modelling
• Difference between data modeling and logical
  database design
• Four roles of data modelling in cadastral system
• Updating and Upgrading of the DCDB
• Graphically Accurate and Survey Accurate DCDBs
• Isolated Survey process supports a Graphically
  Accurate DCDB
• Coordinated Survey process supports a Survey
  Accurate DCDB as part of a Coordinated Cadastre

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Exam Questions

• Distinguish between data modeling and logical
  database design
• Describe the roles of cadastral data modeling in
  cadastral systems.
• Distinguish between isolated survey data model
  and coordinated survey data model.
• Distinguish between upgrading and updating
  Digital Cadastral Databases. Give two examples
  for each of the processes.
• Choose two of the following entities and briefly
  indicate their role in the flow of spatial data
  that eventually updates the DCDB of Victoria?
• Local government
• Cadastral Surveyor
• Titles Office, Land Victoria
• Land Information Group, Land Victoria