Pressure causes the iron core of the planet to solidify despite its high temperature. The mantle, under the crust, remains more plastic, allowing the plates of solid rock on the surface to float and slowly move about. The places where these tectonic plates meet become sites of volcanism and mountain building. Other processes also affect the appearance of landscapes. Low lying plains may become bogs and wetlands.
Ice freezes in rocky cracks, splitting the rocks apart.
Planets are constantly undergoing change. Mapping your planet will set the stage for the development of your world. Earth is about 70 per cent covered by water, which ensures plenty of evaporation for clouds and rainfall. Deep oceans permit better circulation of the water, but shallow seas can be warm and life nurturing. Something else to consider is the influence of gravity.