When you have a DEM, you will find mountains and valleys. Would you like to find out more? Let’s make a relative elevation model.

Reveal floodplain with elative elevation model

DEMs tell you a details of the geography of the area. REM, relative elevation model reveal the floodplain clearly.

relative elevation model

Tools

• QGIS

Data sources

• DEM: 国土地理院基盤地図情報
• Centerline of streems: 国土数値情報

How to make

1. Get a DEM and a line data of a stream centerline
2. Construct pointa along the stream line with a proper dense
3. Extract DEM values to the points
4. Run IDW tool and create an interpolated raster from points
5. Calculate Original DEM minus interpolated raster

Visualisation tricks

1. As a base layer, lay hillshade
2. Select multiply mode For the REM layer
3. Strech the color gradation range relatively small like -2 to 20m to highlight the floodplain

References

• Floodplain visualization using lidar-derived relative elevation models