Combining Raster Calculator with elevations
I want to identify which areas of Chetney Marshes would be flooded by a 2m rise in sea level. I used LIDAR data in contour format as the elevation data:-
I am using the TIN method to create an elevation model as the area is relatively small and the data is supplied as contours. TIN’s are more accurate, especially if the source data isn’t in grid format. However they are slower to process, especially over very large areas.
Select Plugins, Interpolation to open the Interpolation dialogue:-
I made the following changes to the display properties:-
- Colour map – Pusedocolour
- Transparency – I set global transparency to 50%
I now have an elevation model of the area. I now use the Raster Calculator to identify each pixel with an elevation of less than 2m. The elevation is stored in the pixel value. The raster calculator will identify each pixel with band value of less than 2.
The expression is elevation < 2
Select Raster, Raster Calculator to open the Raster Calculator:-
To change the Display Properties for a layer, Right click on the Layer in the layers panel (Table of Contents) and select Properties. I made the following changes to the display properties so the areas that are less than 2m, and susceptible to flooding appear highlighted in blue:-
- Style tab: Color map – Colormap
- Transparency: Global transparency 50%
- Colormap tab: I added 2 entries:-
- 0.00 white
- 1.00 blue