The QGIS interface with several layers loaded in
Starting from the base up
Every map begins life as a base map in QGIS. A base map is a reference map that provides geographical context and boundaries in which data can be located. Most GIS software offers a range of base maps that are ready to use, but they can also be imported from external sources. For example, we often use Natural Earth, an open-source map database that has accurate maps at various scales. Map layers are typically vector-based shapefiles. These files store the location, shape and any attribute information of geographical features.
When sourcing shapefiles, it is important to make sure all parts of the file are downloaded for it to display correctly. For a world map like the recent Daily chart on the modelled risk of emerging covid-19 variants, we usually download and display polygons (the shapes) of the land and borders of countries (including any disputed borders) to start with. Extra layers, such as transport networks, mountain ranges or lakes and rivers may also be included depending on the context of the story. Shapefiles are also editable, which can be useful when you want to include additional details.
Adding on the layers
To turn the map into an infographic for The Economist, we add data layers on top of the base map. Any data added to our maps must have a spatial element such as degrees of latitude and longitude, georeferenced imagery (such as geoTIFF files), postcodes or country codes, so that it can connect with the map. Additional data can be imported into QGIS depending on the file type (see below). Point co-ordinate data are added as a delimited text layer with a set geometry definition, TIFF files are added as a raster (or grid) layer, or if the data shares a common field with the base map then we use the join tool to tell QGIS where to assign the data.
Een reactie posten
Opmerking: Alleen leden van deze blog kunnen een reactie posten.