A raster is a rectangular pattern of rows and columns with a spatial georeferentiation. On a raster each cell contains a value that is uniform in the cell geospatial extension and its the most used spatial data model when we deal and analyze spatially distributed values as land cover, precipitation or population density.
Spatial analysis on raster deals with raster resolution or cell size. As smaller the cell size, the result from the analysis will be finer however the raster file size will be much larger; if we use coarse cells, the raster file sizes will be smaller but the results could be poor for the objectives of the analysis. An equilibrium in between the raster resolution and the raster file size has become a topic to have in mind for beginner GIS users as well as for experienced GIS users.
QGIS is a free and powerful Geographical Information Software (GIS) software. QGIS comes with a variety of tools to manage vector and raster spatial data and its capabilities can be increased when it couples with Grass, SAGA GIS, OTB and its plugins. This tutorial show the simple procedure to change the raster resolution in QGIS 3.