Whatever more or less final rectifications of frontiers result from the current war, the land of the Thai will still, for general purposes, fall into four geographic divisions of major importance: Northern, Central, Eastern, and Peninsular.

Northern Thailand, lying between the Salwin and the Me Khong, two of the world's most majestic rivers, is, for the most part, a country of roughly parallel ranges and valleys running north and south. At the heads of the flat-floored valleys, which vary in elevations above sea level from 800 feet in the southeast to 1,200 feet in the northwest, arise important streams, the Me Nan, the Me Yom, the Me Wang, and the Me Ping, which, falling through narrow defiles to debouch in the low land of Central Siam, eventually there conflow to form the Me Nam Chao Phraya, the chief artery of that division. On the alluvia of these streams, as might be expected in a country whose civilization was originally based upon riziculture, live the great bulk of the northern Thai or Lao, in a setting of rich fields and orchards. The ranges similarly rise, southeast to northwest, from low, rounded hills to imposing peaks, many of which exceed an altitude of 5,000 feet and two of which achieve more than 8,000 feet. These mountains, rising abruptly from the valley floors and, on the whole, densely forested, are scarcely inhabited by man except for scattered groups of seminomadic hill tribes, which exist there by hunting and a primitive agriculture. The northernmost province, Chiengrai, is separated from the sister provinces by a mountain wall and belongs wholly to the Me Khong drainage; it is largely a region of marshes and grassy savannas.

Central Siam, the heart of Thailand, is the vast alluvial plain of the Chao Phraya and may be described as 55,000 square miles of almost unbrokenly monotonous scenery. The level of the land is but little higher than that of the sea and, during the dry season, tidal influence is plainly evident as much as 50 miles from the river's mouth. Alluvial deposits, brought in the season of floods from the northern hills, are, however, raising this level at an astonishing rate; geological evidence shows that within comparatively recent times a great part of the plain was covered by the sea and even now the northern shores of the Gulf of Siam, at the mouth of the Chao Phraya, are advancing seaward at a rate of almost a foot a year. Its rich soil, its abundance of watercourses, both natural and artificial, and its comparatively dense population combine to make it one of the most eminently suitable areas of the world for the production of fine rice.

As Central Siam is the heart of the Kingdom, the royal city of Bangkok or Krungthep is the very core of that heart. Situated on the banks of the Chao Phraya, some 20 miles from its mouth, this metropolis, whose history goes back not earlier than the mid-eighteenth century A.D., is the center for scholarship and the arts, the filter through which pass all goods and ideas received by the interior from the outside world, and the nucleus of one of the most highly centralized of national governments. Its citizenry of some 800,000 represents no less than 5 percent of the total population of the country.

Eastern Thailand is a huge, shallow, elevated basin, tilted toward the east, so that while its western rim stands 1,000 feet above the sea, its eastern rim is formed by low hills. The plateau is watered by the system of the Me Nam Mun, a tributary of the Me Khong. A poverty-ridden country of unproductive soil and adverse climatic conditions, it supports indifferently well a comparatively limited population.

Peninsular Siam is the narrow, northern two-thirds of the Malay Peninsula, sharply divided longitudinally by a mountain chain which passes down its whole length. It is a country rich in forests, cattle, fisheries, mines, and agriculture, and possessed of great natural beauty in the countless islets off its shores, its beaches lined with palms and casuarinas, and the verdure of it mountain-backed landscapes. Most of the developed natural wealth of the Kingdom is found in this portion, which has fine systems of highways and railroads.

The whole of Siam lies between the Tropic of Cancer and the Equator and is subject to the typical monsoonal climate of southeastern Asia, by which the prevailing winds, from the latter part of April to the middle of October, consistently blow from the southwest and from mid-October to April, from the northeast. In Northern, Central, and Eastern Thailand there are three distinct seasons—the hot weather, the rains, and the cold weather, the first extending from February or March to May, the second from June to October, and the third covering the remaining months of the year. When the northeast winds blow strongly, the cold weather is very marked, but at such times as the seasonal winds fail, the cold weather is scarcely distinguishable from the hot. In Northern Siam, which lies at greatest distance from the sea and possesses greater radiation, the days may be hot even during the cold weather when the night temperatures afford a strong contrast by dropping to as low as 50° F. and on the mountains even lower, although never reaching freezing temperatures. The basin of Eastern Siam, with its thin vegetation and cut off from cooling breezes by its surrounding rim, is subject to terrific heats during the day and, during the winter, very low temperatures at night. The central plain, outside of Bangkok, is pleasantly cooled during the hottest season by the continuous sea winds, night and day; in Bangkok, however, perhaps owing to houses of masonry in place of thatch and the drainage of surrounding marshes, the climate is not only appallingly hot but actually becoming perceptibly more so year by year. Peninsular Siam has the mildest and most equable climate, the greatest annual rainfall, and only two noticeable seasons—the hot weather from February to August and the rains from September to January, with the peak of the wet season coming in December.

Owing to the fact that the political frontiers have little relationship to biogeographical boundaries, the Kingdom possesses a fauna and flora richer than those of most areas of comparable size. The primeval jungles of the western and northern mountains show untrammeled Nature at her tropical best. The slopes are enlaced with countless streams and waterfalls, from roaring torrents to rills which flow only during and after the rains. In the forests of these hills and valleys, huge epiphyte-laden trees, bound together by vines, shelter such animals as the elephant, the tiger, and the gaur, but so dense is the cover that the presence of large game is more often made known by signs than by actual sight, and only the hunter who is willing to work hard and long is likely to shoot a worth-while trophy. More than 1,000 different birds are recorded from the country, while fishes of almost endless variety abound everywhere, from the Gulf to the smallest roadside ditches. The natural vegetation ranges from the most typically tropical plants, such as the mangosteen, to forms of the Temperate Zone, such as pines and violets, on the northwestern mountains. The central plain, where not devoted to rice cultivation, shows the characteristic flora and fauna of a marsh and the eastern plateau has an impoverished biota, characterized by a certain number of endemic forms; the Peninsula, however, like the west and north, bears great forests rich in species of animals and plants.