The Study Area and Methodolgy

Penang Island

Penang Island, about 300 square kilometers in area, lies in the Indian Ocean about 2.5 km west of the Malaysian mainland. The island is a tourist center, famous for its food, the luxury hotels along the north coast, and its sandy beaches. In fact there are only small patches of beach except in the Holocene areas that emerged from the sea about 5,000 years ago. Along parts of the coast granite rocks reach to the shore. (See: Quaternary geology map.)

Georgetown (G in Figure 3), the state capital and Malaysia's second largest city, is built on Holocene deposits (mostly sand and clay) found along most of the coasts of Penang Island, in places extending up the river valleys where they provide flat areas that can be excavated for building foundations and infrastructure such as water mains, sewers, storm drains, and telephone cables.

The areas close to the ferries to the mainland (F) and the bridge are more urbanized than the western, Indian Ocean side of the island. The Mukim of Bayan Lepas was formerly occupied by farmers who cultivated rice in padi fields, but now the coastal lowlands and Ara River basin are mostly urbanized. For more than thirty years semiconductor chips have been assembled here, so that almost all electronic devices in the world have components from this small area. The study area (white rectangle) is about 67 km² of which 48 km² (70%) is land.

The image in Figure 3 was acquired by the ASTER instument abord TERRA. ASTER described by NASA.

Methodology

The study compares land use in 1969 with land use in 2003 with special emphasis on change from non-urban to urban uses. The base year, 1969, is defined by a topographic map, while the final year, 2003, is defined by set of ASTER satellite images. A digital elevation model (DEM) was also prepared so that changes in land use could be related to topography. (See: Topography.)

The Topographic Map

The land-use map for 1969 was assembled from a series of overlay images, each overlay image representing a single land-use extracted from the topographic map. (Techniques for making 1969 land-use map.)

For example, a graphics program was used to remove all color pixels from the topographic map. What remained were black lines, labels, and symbols, including black squares representing buildings. Every building symbol was replaced with a four-pixel red symbol. All black pixels were then erased and the red symbols for buildings converted to black. The resulting image is a map showing buildings as black symbols a white background. Places of worship are excluded since they are not shown as black squares in the original image. Black rectanges, representing large buildings, were considered to be multiple black squares. (See: Buildings overlay.)