Section outline

    • Introduction

      Depending on the type of research, your study area can be within:

      • an administrative boundary (e.g. country, province, municipality)
      • a semi-natural boundary (e.g. national park, delta)
      • a natural boundary (e.g. catchment, subcatchment, lake)


      You can download GIS data with boundaries from national mapping agencies, Natural Earth, OpenStreetMap or other open data sources. You can also use GIS to digitize or delineate boundaries.


      Boundaries


      National Mapping Agencies

      The first place to look for data is the website of the national mapping agency of the country where you're going to do the fieldwork. If you don't know the name of the national mapping agency, try to Google (e.g. "national mapping agency France"). Then try to find a geoportal or other ways to download data.

      This video shows an example:

      Natural Earth

      Free vector and raster data can be downloaded from Natural Earth:

      OpenStreetMap

      OpenStreetMap (OSM) is a collaborative project to create a free editable map of the world. OSM is considered a prominent example of volunteered geographic information (VGI) or crowdsourcing.
      In QGIS you can download data from OpenStreetMap using the QuickOSM plugin. You can download features using keys and values that are listed on this page: https://wiki.openstreetmap.org/wiki/Map_features.

      For administrative boundaries you can use key = boundaries and value = administrative. In the attribute table you need then filter on the tag of the level that you need. This is explained here.

      For national parks you can use key = boundary and value = natural park.

      A general video on how to use QuickOSM in QGIS to download features in QGIS:

      Digitizing semi-natural boundaries

      Some boundaries, such as river deltas are not well defined. For example, the coast is a clear boundary of a delta. But how far upstream do you choose the apex? In some cases you need to digitize this.

      Here's a video on digitizing vectors in QGIS:

      (Sub)Catchment boundaries

      HydroSHEDS

      For larger basins you can download the HydroBASINS boundaries from HydroSHEDS. HydroSHEDS is a free mapping product that provides hydrographic information for regional and global-scale applications in a consistent format. It offers a suite of geo-referenced data sets (vector & raster) at various scales, including river networks, watershed boundaries, drainage directions, and flow accumulations. HydroSHEDS is based on high-resolution elevation data obtained during a Space Shuttle flight for NASA's Shuttle Radar Topography Mission (SRTM).

      Catchment delineation

      In more detailed field studies you need to delineate the catchment using GIS methods. If you have a name of a river, you can use the GeoCoding plugin to find it. Then trace the river downstream to find the outlet of its catchment.
      You need a Digital Elevation Model (DEM) to delineate the (sub)catchment. This can be downloaded from national mapping agencies. When local data is not available or accessible, you can use open data, such as data from the Shuttle Radar Topography Mission (SRTM). You can download the data from USGS Earth Explorer or use the SRTM Downloader plugin in QGIS.

      Another great way to download DEM data into QGIS is with the OpenTopography DEM Downloader plugin. It will clip the data to a specified extent. Here's how it works:

      This playlist shows different methods for delineating (sub)catchments, including the theory:

      Here we apply it to a study area in France using a 5 m DEM:

      Note that if you have a coordinate or point vector file of an of an outlet you need to make sure the coordinates are in the same projection as your project and you need to snap the point to the delineated stream:
    • Tutorial Stream and Catchment Delineation URL

      There are different tools in QGIS that you can use for stream and catchment delineation: SAGA, GRASS, WhiteBoxTools, PCRaster, etc. Currently the most robust approach is to use the PCRaster Tools plugin.