CoastGIS'99: geomatics and coastal environment
their tools to define limits for the new areas, as well as to propose a new
law with well-defined co-ordinates, for the problematic areas. In the
definition, the boundaries of the areas will be described by simple geometry (fig. 2), similar to that of the reference features used (isobaths,
seagrass meadows, etc.) with all the points georeferenced in sexagesimal
geographic co-ordinates and ED-50.
This decision has been taken for several reasons:
- it would provide better description of boundaries and facilitate ship
positioning;
- the position of a point in the sea is usually expressed in geographical
co-ordinates and fishermen use these co-ordinates;
- it would be more complex to use UTM co-ordinates, because the
Spanish marine area occupies five time zones, zone 27 and 28 in the
Canary islands and zones 29, 30 and 31 in the peninsula and Balearic
islands area, and two zones include several autonomous communities;
- the information in the GIS should be continuous. The use of geographical co-ordinates avoids the problem of time zone changes in the
UTM system and, when it is necessary to work in another system of coordinates, it facilitates projection changes.
Where is the coastline?
The coastline is acomplex ancl difficult element to define. Legally speaking,
it is an important legal limit for different Administrations and it should
be a static element, defined by a line. However, the real coast is dynamic,
as a result of environmental evolution.
In a GIS for coastal management, the coastline is an important limit and
it carries a lut of semantic information (legal, environmental and economic). Therefore, it was the first element to be put into the GIS, but this
rose a new critical issue, because official data sources do not coincide.
According to the cartographic services used as references (IGN and IHM),
the land-sea limit definition differs and the existence of tides complicates
this definition. There is also continuity between an area with tides
(Atlantic) and another without tides (Mediterranean Sea).
Terrestrial cartography and the official Spanish coastline have been
published by the National Geographical Institute (IGN) in UTM projection, but this coastline does not show the intertidal zones. For marine
zones, the official cartography is published by the IHM in Mercator projection, but depending on the area, nautical charts have different scales
and resolutions ancl they indicate as land or intertidal areas all zones that
potentially emerge and therefore may be a danger for sailing. Consequently, these two coastlines differ in many points (fig. 3).
On the other hand, definitions are lacking for the coastline in areas
with tides (in our case the Atlantic and Cantabrian shores), especially
if the coast is smooth, because tidal variations and storms displace it a
lot. The coast, instead of being a line, should be represented as a polygon,
in which important processes are developing. It is also necessary to
consider that the coast of the Iberian peninsula has continuity between
298
their tools to define limits for the new areas, as well as to propose a new
law with well-defined co-ordinates, for the problematic areas. In the
definition, the boundaries of the areas will be described by simple geometry (fig. 2), similar to that of the reference features used (isobaths,
seagrass meadows, etc.) with all the points georeferenced in sexagesimal
geographic co-ordinates and ED-50.
This decision has been taken for several reasons:
- it would provide better description of boundaries and facilitate ship
positioning;
- the position of a point in the sea is usually expressed in geographical
co-ordinates and fishermen use these co-ordinates;
- it would be more complex to use UTM co-ordinates, because the
Spanish marine area occupies five time zones, zone 27 and 28 in the
Canary islands and zones 29, 30 and 31 in the peninsula and Balearic
islands area, and two zones include several autonomous communities;
- the information in the GIS should be continuous. The use of geographical co-ordinates avoids the problem of time zone changes in the
UTM system and, when it is necessary to work in another system of coordinates, it facilitates projection changes.
Where is the coastline?
The coastline is acomplex ancl difficult element to define. Legally speaking,
it is an important legal limit for different Administrations and it should
be a static element, defined by a line. However, the real coast is dynamic,
as a result of environmental evolution.
In a GIS for coastal management, the coastline is an important limit and
it carries a lut of semantic information (legal, environmental and economic). Therefore, it was the first element to be put into the GIS, but this
rose a new critical issue, because official data sources do not coincide.
According to the cartographic services used as references (IGN and IHM),
the land-sea limit definition differs and the existence of tides complicates
this definition. There is also continuity between an area with tides
(Atlantic) and another without tides (Mediterranean Sea).
Terrestrial cartography and the official Spanish coastline have been
published by the National Geographical Institute (IGN) in UTM projection, but this coastline does not show the intertidal zones. For marine
zones, the official cartography is published by the IHM in Mercator projection, but depending on the area, nautical charts have different scales
and resolutions ancl they indicate as land or intertidal areas all zones that
potentially emerge and therefore may be a danger for sailing. Consequently, these two coastlines differ in many points (fig. 3).
On the other hand, definitions are lacking for the coastline in areas
with tides (in our case the Atlantic and Cantabrian shores), especially
if the coast is smooth, because tidal variations and storms displace it a
lot. The coast, instead of being a line, should be represented as a polygon,
in which important processes are developing. It is also necessary to
consider that the coast of the Iberian peninsula has continuity between
298