This map was done for the 2024 #30DayMapChallenge It shows the Willamette River between Corvallis and Salem Oregon. A Relative Elevation Model (REM) is also known as a height above river raster. The DEM is detrended to the baseline elevation of the river. I used the IDW method detailed by Dan Coe Carto: https://dancoecarto.com/creating-rems-in-qgis-the-idw-method