Learn how to start a new TOPKAPI project using MapWindow GIS.
Learn how to locate and define your working area.
Create a shapefile containing your working area and use it to clip thematic maps in your project.
DEM is often organized into tiles. Once you have located your catchment, you can find out which DEM tiles you need in your working area and add them to your project.
Learn how to use the shapefile of your working area to clip shapefile in your project.