The Longest Boundary defining Australias coastline

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The Longest Boundary- defining Australias
coastline

• Bill Hirst David Robertson
• National Mapping Division
• of Geoscience Australia

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Acknowledgements

• Department of Mineral and Petroleum Resources
• Department of Land Administration
• CALM Marine Conservation
• Australian Hydrographic Office

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The longest boundary?
State and Territory Borders
New South Wales 4,635 km Western Australia
1,862 km
Australias Coastline
Approx 36,000 km around the mainland Another
24,000 km around islands
The shortest boundary?
Boundary Islet (Land border between Vic and Tas)
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Defining the coastline
Terms relating to Tidal Levels
LAT
MLW
MHW
MSL
MLWS
MLLW
MHHW
MLWN
MHWS
HAT
MHWN
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Tide Levels and Charted Data
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Common mapping coastlines

• Cadastral Boundaries (land to MHWM)
• Maritime Boundaries (water to low water mark)

National Low Water Datum Australia has adopted
Lowest Astronomical Tide for the purpose of
defining the Territorial Sea (Commonwealth of
Australia Gazette S29 dated 9 February 1983)
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Defining the problem

• Technical Issues
• The mapping of the coastline is ambiguous and
  each time it is captured in digital format, it
  will more than likely conflict with previously
  mapped data.

• Legal Issues
• Many legal boundary descriptions which include
  reference to the coastline are ambiguous and
  create uncertainty as to the true intended
  location of that boundary.

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Technical Issues
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Technical Issues

• The coastline is a physical feature which moves
  over time.
• It is very difficult and costly to map
  accurately (eg survey, aerial photos, satellite
  imagery LADS).
• There are a number of different coastline
  definitions that are used as boundary
  descriptions and each requires mapping (most
  commonly, MHW, MLW LAT).
• These different coastline definitions should not
  cross when overlayed on a single map.
• The depiction of the coastline in a digital
  environment is dependant on the scale of capture
  and possible generalization of the data.

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Technical Issues
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Australian Maritime Boundaries Information System
(AMBIS)
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AMBIS (continued)

• Fundamental purpose is to map the outer limit of
  Australias jurisdictional maritime zones.
• These boundaries are based on the Territorial
  Sea Baseline (TSB) which consists of the line of
  Lowest Astronomical Tide, straight baselines, as
  well as, bay and river closing lines.
• In practice, only a subset of critical points on
  the coastline (LAT) are required to compute the
  boundaries.
• However, we have found a user demand for the use
  of the TSB as a low water coastline with other
  datasets (in the absence of any better data ??).

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AMBIS (continued)

• Issues arise because of scale, accuracy,
  generalisation and incomplete data.
• The basic premise is that a line of LAT should
  always be seaward of any other depiction of the
  coastline.

In maintaining AMBIS, Geoscience Australia has
used the following general criteria

• Generally committed to best available
  information.
• Need to ensure data have integrity (attributed).
• LAT is seaward within pragmatic uncertainty
  limitations.

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Legal Issues

• Many different definitions of the coastline are
  used in legislation (ie. References to LAT, MLW,
  MHW etc).
• Sometimes there is simply a reference to the
  coastline or low water which creates
  ambiguity in the legislation.
• Attempts (in the Commonwealth, at least) for
  mapping and charting experts to provide
  assistance to those responsible for drafting
  legislation.

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ICSM Activities

• To research the range of definitions that
  describe the boundary between the land and the
  sea, where they originate from and why they are
  used, with particular reference to the Australian
  situation.
• To produce a compendium of definitions in use.
• To provide advice as to the practicality of
  realising these definitions on the ground and/or
  in a digital environment.
• To prepare arguments as to why and how the number
  of boundary descriptions should be rationalised.
• To make recommendations on the minimum number of
  land/sea boundary definitions that might
  realistically be used to describe, visualise and
  realise land/sea boundaries, particularly in
  Australian legislation.

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Summary

• Can the inconsistency between different
  coastline data be resolved? Does it matter?
• Is it possible (or desirable) to achieve one
  digital coastline representation?
• If so, should this be a nationally recognised
  dataset (for example, endorsed by ICSM the
  place names gazetteer is an example of how this
  might work).

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THANKYOU