Page123

SPOT-X image of Bangladesh before the 1988 floods

A more effective method would be to display the extent of flooding on top of the 1987 image. This is the way helpers on the field estimate endangered areas, to assist when making decisions during disaster management.
 
 

	Theme properties

Open the image bangladesh_881010.tif in LEOWorks and click on GIS. Choose File>New Theme, name the theme 'flood', and select Polygon. To start drawing, select Edit>Start Edit.

Digitalise the main river bed. When you are done, choose Edit>Stop Edit to stop drawing. Save the shapefile in your folder 'Monsoon'.

We will now use the image from 1987 and the shapefile for the 1988 flood in the programme ArcExplorer.

ArcExplorer is a lightweight GIS data viewer developed by ESRI. This freely available software offers an easy way to perform basic GIS functions. ArcExplorer is used for a variety of display, query, and data retrieval applications, and supports a wide variety of standard data sources. It can be used on its own with local data sets, or as a client for Internet data and map servers.

Download ArcExplorer (see link in right navigation bar).
 
 

SPOT-X image of Bangladesh after the 1988 floods

Open the ArcExplorer programme.

Choose Theme>Add Theme.... Choose the folder Monsoon and select the image bangladesh_870109.tif. Now select the vector-file Flood.shp produced in LEOWorks.

Both files appear in the ArcExplorer Local box. Tick the boxes to the left of the filenames.

Double click on the file Flood in the Local box. Choose Cross fill for Style and change the colour to blue.

The extension of the flood is now merged with the 87 SPOT XS image. The variation between low and high water levels is visualised, and an enormous difference can be seen. The consequences of this type of flooding are easy to envisage, particularly if they take place in densly populated areas.

Page123