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Application of GIS technology for Coastal Zone Management: a hydrographer perspective
Horizontal and Vertical Datum
Map datums refer to the various locations from where geographic measurements are referenced and this is one of the parameters in which individual maps are identified. Many navigational maps/charts will soon be converted to new horizontal datum known as WGS 84. The use of new horizontal datum has meant that maps/charts that are based on Everest datum can be shifted as much as 150 metres in the horizontal direction as compared with WGS 84 based maps that cover the same area. Conversion programmes are available that can update the horizontal position of present maps to match the horizontal position of WGS 84 maps.
Along with horizontal datum, maps are also referenced to vertical datum, which is the level surface to which elevations are referred. In hydrography the vertical datum is known as chart datum. Another type of datum generally used is the MSL(Mean Sea Level), which is based on the average height of the sea’s surface for the complete tidal ranges over a 19 year period.
Metadata
GIS data normally comes with a file of information that describe the contents of the data sets. This particular GIS information file is commonly known as Metadata and it describe the basic features of the GIS data. For the metadata to be useful, it should list the map title, spatial area covered, the map projection, the horizontal and vertical datum, the map unit, the date of map, mapping specification and accuracy limits.
Information requirements for coastal management
In order to be of any value, it is necessary that the information products output from a CZMs should correspond with the actual requirements of the various user communities. But what are these information requirements? Given a number of potential users of coastal zone data and information, what are the main areas of common interest – or significant diversity – regarding both information desired, and the data needed to be processed in order to obtain that information? The various informations required for achieving the goal of an effective management of the coastal zone could be categorised broadly under following headings.
Data Required for Coastal Zone Information
Geographical data: an organised, planned and coherent coastal database should therefore a basic requirement of a good and constant management. Many of the data to be found within a coastal management database will be geographic in nature and can be called a Geographical data. It is a “data, which refers specially to features that describe the earth’s surface”. Geographical data has both location and attributes. This is the Where something is and the What it is. We can define the where something is as the Spatial component of data, and what something is as the Aspatial or Attribute component of data.
| HABITATS |
COAST |
TRANSPORT |
Estuaries
Sea grass
Macro algae
Inter-tidal
Salt-marsh
Mangroves
Waders
Rookeries
Shellfish
All |
Sandy Beach
Rocky beach
Rocky cliff
Inter-tidal
Mangroves
Salt marsh
Others
All |
Roads(major)
Roads (minor)
Major Ports
Harbours
Marinas
Boat ramps
Airports
Nav channel
Nav Markers
Ferry routes
All |
- Spatial data: It is an explicit spatial/locational reference and can involve absolute or relative locations. These are often referred to as point, lines, areas, or surfaces or can refer to some attribute that is continuous (e.g. elevation), or discrete (e.g. Male/Female or soil categories).
- Attribute Data: Attribute data describes what is a some location and has some link between it and the spatial data.
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