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Census Geography Working Paper 96/3 - 1996 Census Digital Geography Technical Information Paper
 
 


Census Working Paper 96/3

1996 Census Digital Geography Technical Information Paper


INTRODUCTION

Digital computer maps were used to prepare the 1996 Census collectors' maps. These data are also the source of digital map data used in 1996 Census products.


This information paper explains how the digital map data were created and used. The paper was prepared by Martin Brady of the ABS, with contributions from John Allen and Anthony Davis of the ABS, and John Mobbs, of the Public Sector Mapping Authority (PSMA).


Part A provides a broad picture of the 1996 Census digital geographic data and products. Part B contains more detailed information about how the various digital datasets were produced. Part C contains details of 1996 Census geographic products. For readers requiring a historical context, see Appendix A.
Italicised terms are defined in the publication 1996 Census Dictionary (2901.2). Note that only the first occurrence of these terms is italicised.


PART A - OVERVIEW

CENSUS DIGITAL GEOGRAPHIC INFORMATION

The ABS has made available vector based digital geographic information for the Australian Census of Population and Housing (the Census) in various forms since the 1976 Census. Before the 1996 Census the purpose of this
digital geographic information has been to facilitate display and analysis of census and other ABS data in desktop mapping packages and geographic information systems (GIS). The 1996 Census has seen some major steps forward for the ABS in the way that digital geographic information is produced and used by the Census Program.

The ABS has, for the first time, been directly involved with the preparation of digital geographic information used in the 1996 Census. The first use of these data was in the Collection Mapping System (CMS), where digital boundaries for the Census Collection Management Areas were produced based on an underlying digital base map. The digital boundaries created in the CMS were then used in conjunction with the digital base map to produce high quality census collection maps for census field workers.

The second use for the digital base map, boundaries and associated aspatial data (attributes) has been in many of the geographic products produced for the 1996 Census. For example, the boundaries for collection management areas created by the CMS are used to create digital boundaries for the Census Geographic Areas (listed in Appendix C), for which census statistical data are disseminated. The common link between collection areas and Census Geographic Areas is the Census Collection District (CD).

CENSUS COLLECTION MAPPING SYSTEM (CMS)

The base map used in the CMS had to provide a seamless coverage of the whole of Australia. It also had to contain sufficiently detailed topographic and cadastral features to allow accurate definition of the collection boundaries by the boundary designers as well as fulfil specific requirements for use in the collection maps, such as determining collector routes.
The Public Sector Mapping Agencies (PSMA), Candata, and the ABS, cooperated in a joint project to produce a digital base map that fulfilled these requirements.

The development and execution of this project has been one of Australia's largest involving digital geographic information of this type. Through the direct involvement of the ABS in this project, and as a result of the precise census collection requirements, the quality and detail of the digital geographic information produced is unsurpassed by any similar dataset covering the whole of Australia.

The system was built and used to facilitate:
  • the design of collection boundaries;
  • the production of census collection management area maps which integrated the collection boundaries and the base map data;
  • management of the information associated with boundaries; and
  • storage of the digital geographic information used.

The CMS used the following software to manage and manipulate the data:
  • Oracle, as its primary database management system;
  • Intergraph's MicroStation, as the graphics engine; and
  • MicroStation Modular GIS Environment System (MGE), to link the spatial data to the aspatial data.

The digital geographic information produced, including the base map, was incorporated into the Master Spatial Database (MSD).
These same data will be used as input into the collection design process for the 2001 Census.
Appendix B contains more detail about the CMS.

SPATIAL DATABASES

ABS digital boundaries and associated aspatial data have been combined with the PSMA base map to create an integrated dataset called the Master Spatial Database (MSD). In its entirety, the MSD contains approximately 6 gigabytes of data. The ABS has produced three output databases from the MSD. These three databases are the source of the 1996 Census Digital Geographic Information Products.

Output Spatial Database (OSD)
This contains all the data in the MSD except the digital cadastral data and the census collection management area boundaries. The majority of features contained in the database are named by proximate text elements, which are stored as distinct graphic elements in the database. Some topographical features are also attributed with name and feature-classification details. The OSD is approximately 5 gigabytes in size.

At the time of printing this publication, the OSD requires further enhancement before it is possible to derive products of an acceptable quality.

Reduced Output Spatial Database (ROSD)
This contains a selected range of topographic features from the OSD (features have been selected based on their usefulness when used in conjunction with census statistical data and digital boundaries). These selected features have been filtered, that is they have been reprocessed and the number of points per linear and area feature has been reduced, to reduce their storage size. The CD boundaries have also been filtered to an average of 2,000 points per boundary. Boundaries for the other Census Geographic Areas have also been filtered.

For users of MapInfo and other mapping packages which limit the number of points which a polygon can contain, some of the higher level boundaries (for example Statistical Subdivision and higher) will exceed the capacity of the software. In this case Shapes boundaries should be used. In the case of CDATA96, such boundaries will be further filtered so that they can be displayed in MapInfo, however, boundaries so filtered will not align with the CD boundaries or the base map features accurately.
Following the initial creation of this database, significant resources have been put into enhancing the quality of the ROSD.
Additional name attribution has been added to the features in the database. Note that street addresses and street address range data are not available in this database nor any other ABS product. The total size of the ROSD is about 650 megabytes.

Shapes Output Spatial Database (SOSD)
This contains a set of digital boundaries for the Census Geographic Areas that have been greatly filtered to create approximate representation of boundaries. These shape boundaries are intended for use only in low-end mapping packages, such as those included in Excel 95 and Lotus 1–2–3. Boundaries in this database have been reduced to an average of 200 points. This database does not include any digital base map data.

For more detail about the ABS Spatial Databases see Part B below.

PRODUCTS

The ABS has endeavoured to ensure that the data produced provide the maximum benefit to the Australian community. The following products are sourced from the databases discussed above:
  • 1996 Census All-Points Boundaries - These boundaries are sourced from the OSD. At the time of printing this publication, the OSD requires further enhancement before products of suitable quality can be produced.

  • 1996 ABS/PSMA All-Points Base Map - The PSMA may make this product available (refer to the contact list at Appendix I).

  • 1996 Census Reduced Boundaries - This product incorporates the full range of boundaries for which census statistical data are available. Although the detail has been reduced from the original, these boundaries are still highly accurate. Whether used alone, or in conjunction with the matching ABS/PSMA base map, they provide the most accurate base for displaying ABS Census data ever provided. They are suitable for use in many applications.

    These boundaries are sourced from the ROSD. In terms of amount of data, these boundaries are roughly comparable to the 'Standard' boundaries provided from the 1991 Census. The accuracy, however, is significantly better.

    For users of GIS or Mapping Systems which do not limit of the number of points per polygon or region, all higher level aggregated boundaries (for example. Statistical Divisions) align exactly with the CDs in this product. The equivalent boundaries from the 1991 product did not because of CDATA91 system limitations. For users of MapInfo and other mapping packages which limit the number of points which a polygon can contain, some of the higher level boundaries (for example Statistical Subdivision and higher) will exceed the capacity of the software. In this case Shapes boundaries should be used. For MapInfo, a special set of further reduced boundaries are available for the affected higher level areas - these boundaries are more accurate than Shapes boundaries but will not accurately fit the Reduced CD boundaries or the ABS/PSMA Reduced Base Map. For other software with point capacity limitations, either the special MapInfo set (above), or Shapes boundaries can be used.

  • 1996 ABS/PSMA Reduced Base Map - This product has been tailored for use in providing census data users with a highly accurate and detailed digital map. It is also suitable for other applications requiring a digital base map. The PSMA may make this product available (see Appendix I).

    The feature and point reduction which has occurred in the production of this database reduces it to a manageable size. The point reduction employed has had little effect on the overall accuracy of the product.

    It incorporates all the topographic features contained in the ROSD set. The base map aligns with the 1996 Census Reduced Boundaries. These base map data are roughly comparable to the detailed base map data available with CDATA91.

  • 1996 Census Shapes Boundaries - This product incorporates the full range of boundaries, for which census statistical data are available, at a greatly reduced level of detail. These boundaries are sourced from the SOSD.

  • CDATA96 - This product incorporates 1996 Census Reduced Boundaries, Census aspatial and statistical data, and software which supports the display and analysis of the geographic and statistical data. Limited information from the 1996 ABS/PSMA Reduced Base Map is also provided in the standard version. The complete 1996 ABS/PSMA Reduced Base Map is also available as an add-on module. For information about the use of more detailed base map data with CDATA96, contact the ABS (see Appendix I).

  • MapInfo is the mapping engine in CDATA96. MapInfo limits the number of points which a polygon can contain, some of the higher level boundaries (for example Statistical Subdivision and higher) exceed the capacity of the software. In CDATA96, such boundaries will be further filtered so that they can be displayed in MapInfo, however, boundaries so filtered will not align with the CD boundaries or the base map features accurately.

  • 1996 Census Standard Reference Maps - There are two types of full colour reference maps available 1996 Census Collection District (CD) Maps and 1996 Census Statistical Local Area (SLA) Maps. CD maps show the location and coverage of each 1996 Census Collection District (CD) — fully detailed topographic features, including names (e.g. street names) are also mapped.

  • Maps in 1996 Census publications - The 1996 Census Social Atlas series and several of the 1996 Census statistical publications contain maps which use 1996 Census digital geographic information.

  • ABS Client Services - A range of services is available that incorporates 1996 Census digital geographic information, including customised geographic data reports, customised thematic maps and customised reference maps.

The 1996 Census Boundaries, listed above, are available to ABS clients in standard industry formats from a network of secondary providers licensed by the ABS to distribute these products. The ABS/PSMA Reduced Base Map is available as an add-on module in CDATA96. The ABS/PSMA All-Points and Reduced Base Maps may also be available separately from the PSMA. A list of secondary providers can be obtained from the ABS (see Appendix I).

For more detail about census products which incorporate 1996 Census digital geographic information, see Part C below.



MAJOR CHANGES FOR THE 1996 CENSUS

Before the 1996 Census, the ABS produced digital geographic information to add further value to the data coming from the Census and many of its other data collections. This digital geographic information had very few other uses. Appendix A outlines the ways in which digital geographic information has been prepared and used in the past, as well as a broad outline of other geographic products from previous censuses.

The ABS has made some significant advances in the use of digital geographic information in the collection and dissemination of 1996 Census data. These steps forward are either directly or indirectly a result of changes to the census collection mapping program that were implemented shortly after the 1991 Census.



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