In this database, we have created two topological layers stored under the same file. We have used the layer (theme 50) on land parcels for most of our analysis, and the other layer (theme 90) on contours.

Contour lines form closed polygons which could be nested within each other. By building a topological layer for the contours, we can delineate areas within a certain elevation range. We will use the two layers to find the properties that could be affected if the water from the river rises to 8 metres. In 1973, a record-high flood in Fredericton reached a level of 8.6 metres while in 1979, the second-highest flood reached 8 metres. The following picture showing the water level markers was taken during the 1994 flood.

 

 

 

 

 

Generate a buffer zone of areas at or lower than 8 metres.

1. Disconnect the DB Manager since we do not have user-defined attributes for contours.

2. Display theme 90 for contours.

3. Select these two polygons covering the area at or under 8 metres.

4. Select the Utilities > Zone > Create > By Polygons ... menu item to create a zone from the selected polygons. Use a resolution of one metre and call the zone FLOOD.