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TM data
ITIN, it has
ter storage
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's several
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ical DTM
ope-aspect
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ethod (e.g.
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en interval
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ich needs
or interval,
Slope-Aspect Mapping. This is one of the basic
elements for analyzing and visualizing terrain
characteristics. This function is often included in a
standard GIS software, e.g. ESRI's Arc/Info. The
slope and aspect can be computed quite straight
forward from TIN data. Each triangle has three
nodes, normal vector of triangle can be calculated.
Then the slope and aspect can be generated from
directional angles of the normal vector (Alias, 1992).
STUDY AREA
The study area is Langkawi Island, situated in the
north west of peninsular Malaysia. It is an island of
undulated terrain. The study area cover an area of
approximately 32,200 hectares. Two sheets of
topographic map at scale of 1:25000 were used.
Contour lines from this maps were captured by
manual digitizing to form a digital contours. This is
the main DTM data in the project. Other information
such as road network, rivers, landuses, shorelines,
reserved forest, tourist and residential areas were
also extracted from the topographic maps and other
available maps.
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Figure 2 Location map of the study area.
METHOD
The goal of this project is to identify the most
developable land for the selected area (see the study
area). To achieve this goal, two main processes were
carried out, namely, DTM generation, and the
overlay operation. The overlay and buffering
operation is done by using a standard GIS functions.
The following development criteria were used for
land identification.
* Built-up areas.
Only the outside of this area is
considered as developable land.
* Reserved forest areas.
This is one of the protected area.
Physical development is not allowed in
this government reserved area.
e Existing historical, recreational (e.g. golf
fields) and tourist areas.
Only the outside of this area is
considered developable.
e Any areas with surface slope < 20 degrees.
Slope of the earth surface has been
considered as one of the important
restrictions in physical land
development. This measure has been
imposed by the housing authority.
Building constructions on the slope
surface is only allowed within this
slope category.
This list of criteria is not comprehensive, but it's
enough and meet our project's goal. The next section
describes the two main processes in detail.
DTM Generation
Digital terrain models were generated from contours.
The contours of 20 meter-interval were digitized
from the existing topographic maps. A commercial
DTM program, ie. TIN Surface Modelling of
Arc/Info software was used to generate the TIN-
based DTM.
Topographic
Map
Y
Manual
Digitizing
Editing
Arc/Info
TIN
€ Contours
Aspect map
Slope map
Figure 3 DTM generation flow
The entire study area has created 150,000 triangles
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
