Water Corporation takeon Referential Topology

WALIS Referential Topology Workshop April 09

Presenter: David Bulfield

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Cadastral Re-alignment Project

• What is the Cadastral Re-alignment Proposal ?– It is a misnomer for an asset re-alignment exercise to shift the

locations of some 3+million asset records to a new set of cadastral boundaries across the State.

• Land base is maintained independently by Water Corporation based on proposed subdivision & Development activity

• Asset information is plotted in relation to proposed or actual parcel edges and road casements.

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What is different with a Utility

• We deal almost exclusively with linear and point objects

• Generally, objects are related to but not necessarily linked (snapped) to boundary offsets.

• Every spatial shift of a parcel edge corner results in shift vectors applying to every “related” object.

• Changing lengths of linear objects can’t always be reconciled.

• And we still have to contend with polygon slivers from static boundary layers (eg; Loc Govt, MRS etc ..)

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(not) Just another map!

WaterWaterSewerSewer

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Conflict in Our Business Needs

Submit Development Application to

DPI

DPI Refers to Agencies for

comment

Applicant submits

proposed asset details for approval

Engineering/precalc survey

revisions

Deposit Plan at Landgate

WAPC Final Approval

Data captured into GIS – continually revised & updated from Survey information

Landgate capture data from lodged survey plans.

Current lodged survey plans applicable until this point

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The Cadastral relativity problem• Data was originally digitised from hardcopy plans at various

scales with a resulting low degree of spatial accuracy.

• ~1992, the Water Corporation stopped utilising spatial updates from the authoritative Landgate database and maintained data in isolation.

• Landgate continued to improve accuracy of its SCDB.

• Adhoc acquisitions of data from Landgate in outlying urban areas revealed a growing disparity with Core Land data.

• Recent expansion (explosion) of digital data requests and experienced GIS users indicates customers may not be as willing to “warp” our data to fit theirs.

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Examples of current data variation

Figure 1

Example of variation of road centreline to parcel edges. - Boyanup

Road centreline - Green

Parcel edges - Black

Figure 2

Example of parcel edge variation Landgate to Water Corporation. - Boyanup

Landgate - Blue

Water Corporation - Black

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Another example

Road centre-line

Our street location

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Issues with Boundary Offset Relationships

2.5m offset from corner

Note change in pipe length

!

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So, What’s the point?

• If we never share our data – keep it to ourselves, then we don’t need to do anything.

• Why not just ignore the impact on others and our own data capture issues and continue as before.

• Why not just delete all the land and start again.

• Someone else has done this before – why not ask them why they did it (& how)?

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Our Project - Progress to date

• Phase 1 - Feasibility completed– Identified a significant impact on the business

when comparing our asset locations against other external datasets.

– Identified at least 17 prospective toolsets ostensibly covering the land base alignment process.

• Phase 2 - toolset evaluation pilot, cost and revised process discovery just started.

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Other takeaways!

• Regardless of the known, accurate absolute location of our assets, we are obliged to relate asset location to cadastre.

• Use of Imagery greatly increases the perception of land base error.

• There is a product discrepancy between source data and user’s required accuracies.

• Dependent customer agencies should not be subjected to unnecessary “shifts”.

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THANK YOU