Trilla is a warm temperate world that lacks polar ice caps and would once have possessed large bands of rainforest in its equatorial regions.  The land area of the world is dominated by three large continents.

The largest of these is the continent of Magora, which stretches from the North Pole to around 30 degrees south of the equator and covers almost half of the land area of Trilla.  As a result of its large span of latitudes Magora has the most diverse range of environments of Trilla’s three continents with tundra and steppes in the northern polar region and hot, wet, tropical conditions near the equator.  The largest environmental region of Magora is a broad temperate belt in the northern mid-latitudes that experiences moderate rainfall and relatively mild temperatures.  A large part of this temperate belt lies within the drainage basin of the Etray River, by a considerable margin the largest and longest river on Trilla.  Considerable stretches of the Etray and some of its tributaries are deep and wide enough that they are navigable by large grain barges and form an important part of the transport network of Magora.  Magora is crossed by a number of large mountain ranges, the longest being the Severine range that stretches from the polar region diagonally across the continent to the mid-latitudes.  The source of the Etray River lies in the Severine range.

Somewhat further around the globe lies the continent of Hantor, the smallest of the three main continents.  Hantor lies almost entirely in the tropical region of Trilla and is dominated by very fertile land with high rainfall.  As a result of this high rainfall Hantor has a large number of rivers, many of which rise in the Deyadar Mountains that run almost parallel to the Equator through the centre of the continent.  The Deyadar range widens in the interior of the continent and a significant part of the central regions are dominated by the mountains and their foothills.

In the southern hemisphere lies the Naros continent.  Naros has a very irregular shape and, particularly on its western coastline, is surrounded by many islands and island chains.  A few of these islands are very large and some old charts refer to the two very closely spaced islands of Juna and Islay as forming a small separate continent.  Many of the island chains lie in stretches of very shallow sea making them ideal as the backbone of large algae farms and aquaculture facilities.  The main landmass of Naros is largely temperate with a smallish tropical band along the northern coastline of the continent.  There is also a substantial arid region, the Missal, in the south-east of the continent, resulting from the rain-shadow of the Uighur and Ucal mountain ranges, and tundra conditions in the extreme south of the continent.

All of Trilla’s continents show signs of terraforming in the way of terrain smoothing, with steep valleys filled in and ranges of small hills flattened.  The present rainfall patterns are also not quite the same as would occur naturally due to the influence of chemical rain-inducement rockets and air current modification by the orbital laser facilities.  The question regularly arises amongst the Adeptus Mechanicus as to whether it would be possible to increase the rainfall in the Missal region of Naros and make it more productive.  The conclusion is always reached however that the expense of doing so would outweigh the gains in production.