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Mapping realities challenging

Ioane Burese
Wednesday, March 30, 2011

PACIFIC Island countries and territories are challenged by the necessity to update their maps to reflect the present day realities.

"Countries are utilising several mapping systems, or projections, in parallel," said Dr Wolf Forstreuter, SOPAC's Remote Sensing and Geographic Information Systems (GIS) specialist.

"For example, road networks, river systems, coastlines, contour lines and village locations are available on different maps.

"Often each has different accuracy and a different projection. They do not overlay or fit one on top of the other."

Dr Forstreuter said discrepancies were the result of several factors รน mapping carried out by the first surveyors at the end of the 19th century; tectonic shift, which contributes to islands shifting position; legal challenges associated with old maps, and the need for lands departments to move to the use of remote sensing data and new software.

By the end of the 19th century, surveyors had developed grid systems covering parts of Europe.

When the first mapping of island countries took place, a grid system was created for each island that had no reference point to any existing maps, as there were no orientation points to link to another point of an existing mapping system.

"Often legal ownership is based on these old maps and old systems," said Dr Forstreuter.

He said the islands were not stable but moving because of two different reasons.

The first is tectonic shift, an effect that is visible in Tonga, or the very recent case of Japan when the whole country shifted two metres within a few hours.

Secondly, the coastal ocean currents can drift sand away from one side of a small island and settle it on another.

"Today, previously existing land parcels on one side of an island may be in the ocean, while on the other side new land exists without ownership.

"Often lands departments deal with maps where land parcels do not fit the actual river system, or with maps where the island has drifted away."

A related issue in many Pacific Island countries and territories is that Global Positioning Systems (GPS) equipment is not recognised as legal surveying equipment, despite the accuracy that satellite technology makes available.

"Consequently, surveys have to be carried out in traditional ways, supported by the analysis of aerial photography," Dr Forstreuter said.

Traditionally, lands departments have been the only source of mapping in a country.

Dr Forstreuter said since the year 2000, space borne image data, or satellite imagery, has been available for mapping at a scale of 1:10,000, and that GIS and image data software have become so user friendly that it is not necessary to have a background in surveying to use these.

Satellite sensors work in way similar to a photocopier, so the image is not distorted.

The user can map on the computer screen immediately using satellite information and images.





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