Sri Lanka is located at the southern point of the Indian sub-continent, between 5° 54′ and 9° 52′ North Latitude and 79° 39′ and 81° 53′ East Longitude. Its land area is 6,570,134 ha. Topographically, the island consists of a south central mountainous region which rises to an elevation of 2500 m, surrounded by broad lowland plains at an elevation of 0 – 75 m above sea level. From the mountainous region nine major rivers and 94 other rivers drain across the lowlands into the Indian Ocean.
The climate is tropical overall, but it shows variations across the island due mainly to differences in rainfall and elevation. The rainfall shows seasonal fluctuations and is dependent on the southwest and northeast monsoons and on convectional and cyclonic effects. The mean temperature in the lowland areas is 270C in the wet region and 300C in the dry zone. It decreases with increase in altitude, and in the montane region the mean monthly temperature varies from 130C to 160C, with the night temperature occasionally dropping to around zero.
The country has been divided into climatic regions in many different ways. Generally three broad climatic regions are recognized: the wet zone, dry zone and intermediate zone. Whereas the dry zone is all lowland, the other two zones are further subdivided on the basis of altitude. Further, the Island can be divided into a large number of agro-ecological regions based on the combination of the annual rainfall and its seasonal distribution and the altitude.
Geologically, 90 per cent of the island consists of Precambrian crystalline rocks. The other main rock types are Miocene limestone deposits that extend from the Jaffna peninsula and the adjoining offshore islands to the northwest coast as far as Puttalam and down the northeast coast to Mullaitivu, and a small area of Jurassic deposits at Tabbowa andw Andigama, near Puttalam. The overlying soils are of many different types, but the red-yellow podzolic soils (lateritic red loams) in the wet region and reddish brown earths in the dry zone are the most common.
Geomorphologically, Sri Lanka is part of the ancient continent of Gondwanaland. India and Sri Lanka broke off from the disintegrating continent as what is called the Deccan Plate, and, as this plate drifted northwards, the two countries became isolated around 20 million years ago. Sri Lanka has retained its present outline for the last ten million years, since the end of the Miocene. Today, Sri Lanka is separated from India by the narrow Palk Strait, but it is likely that there had been oscillations of the relative levels of the land and sea resulting in land connections with India for short periods.
Sri Lanka, despite its small size, has a rich diversity of soils. Fourteen of the Great Soil Groups have been recognized within the country. The Great Soil Groups in the dry zone and the drier part of the intermediate zone are Reddish Brown Earths (occupying the largest area), Low Humic Gley Soils, Non-calcic Brown Soils, Red-Yellow Latosols, Alluvial Soils (in the flood plains of the larger rivers), soils of the Old Alluvium, Solodized Solonetz (in the arid areas), Regosols (in the coastal areas), and Grumusols and Rendzinas which are found in relatively small extents.
The Great Soil Groups in the wet zone and in the wetter parts of the intermediate zone are the Red-Yellow Podzolic Soils (which is the dominant type), Reddish Brown Latosolic Soils, Immature Brown Loams and Bog and Half-bog Soils (found mainly in the tidal marshes).