System concept and development by:

1
c-squares - a new method for representing,
querying, displaying and exchanging dataset
spatial extents
System concept and development by Tony
Rees Divisional Data Centre CSIRO Marine
Research, Australia
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some example Metadatabases (Data Directories)
many others -- 100 lt 1000? ...

• Typical features include searchability by
• text
• keywords
• spatial and time constraints
• This presentation - focus on spatial searching

3
current base level representation of spatial
data coverage in metadata is by bounding box
(minimum bounding rectangle, MBR)

• concept introduced in 1994 (FGDC)
• used for spatial searching, 1995 onwards
• still the primary tool for metadata spatial
  searches

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How well do MBRs represent spatial
data? (examples from our own metadata system)
MBR actual data locations
Franklin 02/1999 hydrology data
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alternatives to MBRs for representation of data
spatial extents ...

• bounding polygons
• multiple bounding rectangles
• defined regions - countries, administrative
  areas, bio- or geo-regions
• circles (centre point radius)
• pre-defined path distance (e.g. along a
  contour, coastline, satellite path)
• actual point locations held in the metadata
  record
• grid-based system

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global grid systems already available ...

• International Map of the World (IMW) rectangles
  (6 x 4 degrees)
• Marsden Squares (10 x 10 degrees)
• Maidenhead Squares (2 x 1 degree)
• WMO (World Meteorological Organisation) Squares
  (10 x 10 degrees)
• others ?
• -- WMO squares eventually chosen for ease of
  subdivision (base 10) and simple relationship
  between WMO numbers and lat/long values

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WMO 10-degree squares notation (part)
(Available via the web in NODC, 1998 World
Ocean Database 1998 Documentation)
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The c-squares concept c-squares Concise
Spatial Query and Representation System
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c-squares principle
data footprint using bounding rectangle
actual ships track - Franklin voyage 10/87
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c-squares numbering system

• each square is numbered according to a globally
  applicable system based on recursive divisions of
  WMO (World Meteorological organisation) 10-degree
  squares, e.g.
• 10 degree
  square 3414 ( WMO number)
• 5 degree square 34142
• 1 degree square 3414227
• 0.5 degree square
  34142274
• 0.1 degree square
  3414227466
• (etc.)
• strings of codes represent an individual dataset
  extent, e.g.
• 301349731114683111478311147931114883111
  489311149931121223112123
• 311213131121323112134311214131121423112
  143311221731122183112219
• 311222631122353112350311235131123523112
  353311236031123613112362
• 311236331123703112371311238031123813112
  390311310031131013113102
• 311310331131043113205311320631132073113
  216311321731132283113238
• 3113239
• encodes the extent
• shown in the example

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Codes have straightforward relationship with
lats/longs, mapsheets, etc. ...
e.g. 1400458 (1-degree square with origin at
45 º N, 008 º E)
additional degrees E
008 8 additional
degrees N 405 45
5-degree quadrant, i.e. 3 4

1 2 tens of degrees E (i.e., 00)
tens of degrees N (i.e., 40) global sector
(1NE, 3SE, 5SW, 7NW)
46
45
44
110 km
10
8
9
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quad tree -type approach used where numerous
adjacent squares are occupied
squares can be bulked - example 3212
instead of specifying every 1-degree square
within 10 degree square 3212. This leads to
corresponding data reduction, e.g. Australia (at
1-degree resolution) can be described in 343
squares rather than 800
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Example database-level implementation of
c-squares for metadata records (e.g. at 1 degree
resolution)
(etc.)
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Spatial queries using c-squares

• c-squares spatial queries simply test whether a
  text string representing the search box (ideally
  one or several c-squares) is matched anywhere in
  the c-squares string
• example - search square 31132 will match any
  c-squares string which includes 31132 within it,
  e.g.
• ltcsquaresgt
• 311236331123703112371311238031123813112
  390311310031131013113102
• 311310331131043113205311320631132073113
  216311321731132283113238
• 3113239
• lt/csquaresgt
• hierarchical naming system for c-squares means
  that finer resolution squares are automatically
  picked up in any coarser resolution search

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example search result ...
(etc.)
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Viewing the full metadata record produces ...
with clickable link to show dataset extent using
c-squares
(etc.)
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Base maps for displayed data can be changed at
will by the user, e.g.
(numerous other maps available, sample only shown)
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Process invoked for web mapping
c-squares strings can be sent directly to the CMR
c-squares mapper (accessible via the web), e.g.
from OBIS (Ocean Biogeographic Information
System, USA)
ltform action "http//www.marine.csiro.au/cgi-bin
/cs_map.pl" method"post"gt ltINPUT TYPE"hidden"
NAME"csq" VALUE"321545943215459332154594
(etc.)"gt ltINPUT TYPE"hidden" NAME"title"
VALUE"Global Distribution of ltigtRajalt/igt"gt ltINPUT
TYPE"submit" NAME"submit" VALUE"make map
..."gt lt/formgt
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c-squares strings are suitable for inclusion as a
new metadata element alongside bounding box,
for example ...
ltmetadatagt lttitlegtFranklin Voyage FR 10/87 CTD
Datalt/titlegt ltcustodianOrggtCSIRO Marine
Researchlt/custodianOrggt (etc. etc.)
ltboundingBoxgt ltnorthBoundingCoordgt-9.0lt/no
rthBoundingCoordgt ltsouthBoundingCoordgt-19.
0lt/southBoundingCoordgt ltwestBoundingCoordgt
117.0lt/westBoundingCoordgt
lteastBoundingCoordgt145.8lt/eastBoundingCoordgt
lt/boundingBoxgt ltcsquaresgt311149923112390131
1148933112380331123804311238113111488
231123812311237133111478431123704311
237013111478131114792311147913112361
4311146843112363331123613311146723112
360231123631311236223112360131123524
311235233112350431123521311235123112
35223112353231123531lt/csquaresgt (etc.)
would permit interoperability with both enabled
and non-enabled systems
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Summary - strengths and weaknesses of c-squares

• Strengths ...
• c-squares is a concise and flexible method of
  encoding simple to moderately complex forms
• automated or manual code entry (and maintenance)
  is straightforward
• spatial searching is simple text string matching
  operation (no GIS involved)
• c-squares mapper utility available via simple
  web call
• can be used as adjunct to bounding coordinates
  searches
• Weaknesses
• some other numbering systems in use (Marsden
  Squares, Maidenhead Locators) - needs willingness
  to standardise on a single system for
  interoperability
• c-squares are not a fixed multiple of
  kilometres, miles, etc.
• strings can become quite long for large, complex
  regions (e.g. Pacific Ocean) - need to be able
  to incorporate data reduction using bulk method

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other comments ...

• c-squares notation is language-independent -
  can be equally useful in English, French,
  Italian, Japanese also discipline-independent
• downwards-scalability of the c-squares notation
  means that it can be applied to any size region
  (e.g. local level)
• equally applicable to both terrestrial and
  marine data
• uses established standards for nomenclature,
  basis already available via the web (e.g. NODC
  site)

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c-squares current and future status...

• Implemented already in CMRs MarLIN metadata
  system and CAAB taxon dictionary
• concept is available for implementation in any
  other agencies metadata systems without cost or
  technology overhead
• potential to to be recognised as a formal
  metadata element by relevant user communities /
  national bodies
• current CMR c-squares mapper is already
  accessible for general use
• c-squares website constructed as a focal point
  for all c-squares related materials - including
• initial c-squares specification
• connection information to the c-squares mapper
• sample PL/SQL code (to convert lat/long pairs to
  c-squares)
• on-line lat/long - to - c-square converter
• example c-squares-enabled metadata records, and
  more

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• Acknowledgements
• Miroslaw Ryba and other CMR staff for assistance
  with constructing the c-squares mapper and
  general feedback
• Blue Pages Marine and Coastal Data Directory
  (MCDD) for the notation for subdividing WMO
  squares
• Martin Dix (CSIRO Atmospheric Research) and NOAA
  Globe Project for base maps as used in the
  mapper (used by permission)

Questions, comments?
website http//www.marine.csiro.au/csquares/ (NB
handout available at this meeting) My email
Tony.Rees_at_csiro.au