WA LOCAL GOVERNMENT GIS FOCUS GROUP

1
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology
• - the Local Government perspective

2
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology the survey
• Approximately how many tables do you have in your
  GIS database?
• 2. Approximately how many were spatially
  constructed based on the cadastre?
• 3. Approximately how many are spatially
  referenced from aerial photography?
• 4. Approximately how many are spatially absolute
  (surveyed or by GPS)?
• Please comment on the importance of maintaining
  spatial relativity. How much of a problem is it
  if your home-built tables dont exactly
  coincide with the cadastre?
• 6. Do you currently check for slivers or
  overlaps with every cadastral update? Do you
  redefine points, lines and polygons to maintain
  relativity?

3
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology the results
• Digitised from Absolute
• LGA No Cadastre Photography (eg GPS)
• 87 8 5
  0
• 250 A few Most 30
• 194 25 15 5
• 34 11 1
  1
• 121 53 21 0
• 90 17 Many Most
• 120 36 4
  2
• 900 160 250 120

4
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology
• Digitised from Absolute
• LGA No Cadastre A/P GPS IMPORTANCE IP
• 87 8 5 0 1 13
• IMPORTANCE OF SPATIAL CONSISTENCY
• little importance at this stage as all
  information is for reference only. If we require
  more accurate information then a survey is
  requested

5
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology
• Digitised from Absolute
• LGA No Cadastre A/P GPS IMPORTANCE IP
• 2 250 A few Most 30 3 450?
• IMPORTANCE OF SPATIAL CONSISTENCY
• important for users of TPS data as we derive
  data based on spatial constraints.

6
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology
• Digitised from Absolute
• LGA No Cadastre A/P GPS IMPORTANCE IP
• 3 194 25 15 5 4 160
• IMPORTANCE OF SPATIAL CONSISTENCY
• This is a big problem mainly with Planning
  schemes and the like but it occurs with any table
  that uses the cadastre at some point in time as
  its base.

7
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology
• Digitised from Absolute
• LGA No Cadastre A/P GPS IMPORTANCE IP
• 4 34 11 1 1 4 48
• IMPORTANCE OF SPATIAL CONSISTENCY
• Due to the spatial queries within our GIS, if
  the layers dont coincide closely with the
  cadastre, then incorrect/ambiguous details can
  potentially be displayed, so it is very important
  that accurate spatial relativity is maintained. 
  Our corporate GIS viewer allows for an
  approximate tolerance for non-coincident
  boundaries, however it is difficult to find a
  perfect tolerance due to the differing
  alignments across the entire municipal area.

8
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology
• Digitised from Absolute
• LGA No Cadastre A/P GPS IMPORTANCE IP
• 5 121 53 21 0 4 296
• IMPORTANCE OF SPATIAL CONSISTENCY
• Minor at this stage of development. Potentially
  major effect on future automated business
  procedures and results of spatial queries to
  public via Internet.

9
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology
• Digitised from Absolute
• LGA No Cadastre A/P GPS
  IMPORTANCE IP
• 6 90 17 Many Most 4 280?
• IMPORTANCE OF SPATIAL CONSISTENCY
• Issues sometimes occur when doing a spatial
  query from our GIS. The query may sometimes
  return the wrong or multiple zonings, rcoding,
  ODP, DAP, contaminated site or other documents.
  While misalignments can have a tolerance set, it
  is difficult to set something that will work
  across the entire municipality.

10
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology
• Digitised from Absolute
• LGA No Cadastre A/P
  GPS IMPORTANCE IP
• 7 120 36 4 2 3 120
• IMPORTANCE OF SPATIAL CONSISTENCY
• Some of our in-house mapping is significantly
  displaced from the current Landgate cadastre and
  will be corrected over the next 12 to 18 months
  more important mapping such as the Local Planning
  Scheme will have high priority.

11
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology
• TYPICAL PROBLEMS AND COMMENTS
• Inaccurate reporting of constraints based on
  spatial queries
• Inefficient or incomplete workflows generated
• Misleading information provided to Public
• Creates need to realign all tables spatially
  constructed from the cadastre
• Lack of resources to fully QA input from
  trusted source
• Probable impact on SLIP layers spatially based on
  cadastre what version of cadastre was used?
• Is the problem with cadastral updates? Landgates
  stated accuracy usually greater than any spatial
  adjustment.

12
WALOCALGOVERNMENTGIS FOCUS GROUP

• Referential Topology
• Mapinfo 30 LGAs
• ESRI 10 LGAs
• Other 2 LGAs
• Mapinfo does not store attributed primitives
  (points, arcs and vectors) need to deconstruct
  polygons (regions) into a set of topology tables
  before any automated adjustment can occur. Some
  proprietary applications have been developed
  need further investigation.
• GRASS is a topological GIS that can read and
  write Mapinfo tables, is free to use (OpenGIS),
  but requires considerable technical expertise.
• A-Spec demonstrates ability of LGAs to work
  together to implement a new funded project with a
  committed project manager.