Geography is a broad and diverse area of study, a large tree with many branches. The different branches are so different that they tended even in antiquity – with less subject specialization and more polymaths – to be pursued by different people. The main types are (i) human geography, focusing on the landscape of human life, (ii) physical geography, focusing on the land, sea, and sky, and (iii) mathematical geography, focusing on mathematical modelling of aspects of physical and human geography. Where geography and biology meet, we now have ecology and environmental science. This tends in ancient authors to be dealt with under biology and agriculture. The more sophisticated works, such as Theophrastos’ works on botany, consider the effect of geology, soils and microclimates on plant physiology and growth.

Ptolemy practised mathematical geography, and his reconstructed maps often feature as frontispieces in modern books on the history of geography. He scorns human geography of the type written by his predecessor Strabo, much as Thoukudides scorns his predecessor Herodotos’ type of history. We won’t push the analogy while noting that Ptolemy’s Geography is about as much fun to read as a telephone book, which it resembles, strongly. Strabo, for his part, complained that his predecessor Poseidonios’ On the Ocean has too much mathematics and astronomy in it for geographers like himself (so too for would-be writers of geography like Cicero).