WA LOCAL GOVERNMENT GIS FOCUS GROUP

1. WALOCALGOVERNMENTGIS FOCUS GROUP Referential Topology - the Local Government perspective Introduce self Local Government would be the sector with the largest growth potential in GIS To enable a representative view of WA LG GIS, 20 LGAs were surveyed – 6 responses received. Is there a general understanding of “Referential Topology”? Is my definition the same as the next persons? Is a clear and concise statement which can be circulated required? Do they realise they may have a problem?Introduce self Local Government would be the sector with the largest growth potential in GIS To enable a representative view of WA LG GIS, 20 LGAs were surveyed – 6 responses received. Is there a general understanding of “Referential Topology”? Is my definition the same as the next persons? Is a clear and concise statement which can be circulated required? Do they realise they may have a problem?

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 don’t 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? The study asked these questions Q3 begs the question “how was the aerial image georeferenced?” Q6 possibly ambiguous – intended to determine whether spatial tables constructed in-house using the cadastre or aerial photography are checked against the new cadastre.The study asked these questions Q3 begs the question “how was the aerial image georeferenced?” Q6 possibly ambiguous – intended to determine whether spatial tables constructed in-house using the cadastre or aerial photography are checked against the new cadastre.

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 Responses from metro and regional LGAs Average of 120-130 tables each A little under 20% based on cadastre A little over 25% based on aerial photography. Was Photography georeferenced to cadastre? Only 2 LGAs had a significant number of tables derived from surveys or GPS.Responses from metro and regional LGAs Average of 120-130 tables each A little under 20% based on cadastre A little over 25% based on aerial photography. Was Photography georeferenced to cadastre? Only 2 LGAs had a significant number of tables derived from surveys or GPS.

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 Q5 asked for comments on the importance of maintaining spatial relativity. How much of a problem is it if “home-built” tables don’t exactly coincide with the cadastre? Based on the response I have assigned an “importance” factor. Perhaps this factor multiplied by the number of tables digitised (including from aerial photos id georeferenced using cadastre) could give a meaningful number???? Only relative between respondants but???? Importance Product (IP) = 13Q5 asked for comments on the importance of maintaining spatial relativity. How much of a problem is it if “home-built” tables don’t exactly coincide with the cadastre? Based on the response I have assigned an “importance” factor. Perhaps this factor multiplied by the number of tables digitised (including from aerial photos id georeferenced using cadastre) could give a meaningful number???? Only relative between respondants but???? Importance Product (IP) = 13

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. A larger metro LGA Note that most responses note the effect on TPS data tablesA larger metro LGA Note that most responses note the effect on TPS data tables

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. This from a regional centre indicates that those people out there are prety much just like usThis from a regional centre indicates that those people out there are prety much just like us

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 don’t 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. Note the reference to allowed tolerances – more later when we look at accuracy statements in metadata.Note the reference to allowed tolerances – more later when we look at accuracy statements in metadata.

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. Internal advisory systems don’t have to be as robust and comprehensive as services to the public or automated internal systems such as noise complaint investigations, development application processing, generation of workflows in some document management systems.Internal advisory systems don’t have to be as robust and comprehensive as services to the public or automated internal systems such as noise complaint investigations, development application processing, generation of workflows in some document management systems.

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. This response is, I suspect, typical of many LGAs – limited understanding of the problem or this project (and that is not a criticism of them, but a flag that any future group will have to raise the awareness of many users before progressing past these discussions.)This response is, I suspect, typical of many LGAs – limited understanding of the problem or this project (and that is not a criticism of them, but a flag that any future group will have to raise the awareness of many users before progressing past these discussions.)

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? Landgate’s stated accuracy usually greater than any spatial adjustment. Problems noted include :- Note the final comment – the problem is with the relationship between the Landgate cadastre and the in-house tables derived from the cadastre (or the aerial photography georeferenced from the cadastral table). But spatial analysis could be affected to a far greater extent by the accuracy of Landgate’s cadastral data?Problems noted include :- Note the final comment – the problem is with the relationship between the Landgate cadastre and the in-house tables derived from the cadastre (or the aerial photography georeferenced from the cadastral table). But spatial analysis could be affected to a far greater extent by the accuracy of Landgate’s cadastral data?

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. Finally, an overview of the GI Systems used in Local Governments – just the management of GIS data, not necessarily the information delivery application.Finally, an overview of the GI Systems used in Local Governments – just the management of GIS data, not necessarily the information delivery application.