This lecture introduces the concept of isovalue curves, commonly used for various applications such as visualizing terrain with contour lines, as well as in meteorology with isobars, isohyets, or isotherms. These isolines can be easily created through linear interpolation based on any grid of measured or interpolated values. The software QGIS provides a function called 'contour creation' in the 'raster' menu under 'extraction' to implement this operation. The lecture concludes the second week of the course dedicated to continuous spatial phenomena, with the next week focusing on digital elevation models.