When an architect were requested to design a building, he or she MUST visit the potential site as the basic 'homework'. It is where they would gather information in regards of the site that would be use to assist their designing process. Information like the type of existing topography, existing landscape and vegetation, existing access etc etc
For an instance Site A as shown in the first photo could be justify as an easy site to get start with as it's already in its ready-condition to be develop.Site B on the hand would need a whole lot more of studies, and analysis and more information on existing inverts, services etc etc as it has a complex condition to begin the design process.
An architect would have to lead the site study, get as much help as possible, for example a land surveyor need to be appoint to gather all the information of the existing topography, and a civil engineer would be needed for a study on the hills slope and earthwork procedures.
These all would be part of a process being terms as 'Site Study'