Chile extends 4270 kilometers from north to south along South America's western edge while averaging only 177 kilometers in width, making it the world's longest north-south country relative to its east-west dimension. This extraordinary shape creates the most extreme climatic variation within a single nation in the Western Hemisphere, spanning from the driest nonpolar desert on Earth to subpolar oceanic conditions within a single continuous territory. The Andes Mountains form the entire eastern border, rising from sea level to 6893 meters at Ojos del Salado, the world's highest volcano and the planet's second-highest mountain outside Asia. The Pacific Ocean bounds the entire western coast across 6435 kilometers of linear shoreline, though actual coastal length exceeds 78,000 kilometers when accounting for fjords, islands, and peninsulas in the southern regions. Chilean territory includes Easter Island (Rapa Nui), located 3512 kilometers west of Valparaíso, making Chile's economic exclusion zone extend across 120 degrees of longitude despite the mainland spanning only 19 degrees.
The Atacama Desert occupies northern Chile from the Peruvian border near Arica at 18 degrees south latitude to approximately 27 degrees south near Copiapó, covering roughly 105,000 square kilometers. The Quillagua weather station, situated in the Atacama at 970 meters elevation, recorded an average annual precipitation of 0.5 millimeters between 1964 and 2001, with multiple years recording zero measurable precipitation. The Universidad de Chile's atmospheric research indicates certain Atacama locations have received no rain for periods exceeding 400 years based on geological evidence. This aridity results from the cold Humboldt Current offshore creating thermal inversion layers that prevent moisture-bearing clouds from forming, combined with the rain shadow effect of the Andes blocking moisture from the Amazon basin to the east. The Atacama's absolute humidity frequently measures below 0.1 grams per cubic meter, comparable to conditions in Antarctica's Dry Valleys. Temperatures in coastal Atacama locations like Antofagasta (elevation 40 meters) range from average daily minimums of 13°C in July to average daily maximums of 23°C in January, while interior locations at 2500 meters elevation experience minimums below freezing and daytime maximums exceeding 25°C on the same calendar date.
The Altiplano plateau extends into northernmost Chile above 3500 meters elevation, forming the border regions with Bolivia and Argentina between approximately 18 and 27 degrees south latitude. Chilean Altiplano sections include Lauca National Park, where Lake Chungará sits at 4517 meters elevation, and the Salar de Atacama, a 3000-square-kilometer salt flat at 2300 meters that contains 27 percent of the world's lithium reserves according to United States Geological Survey 2022 data. Parinacota volcano (6348 meters) and Pomerape volcano (6282 meters) dominate the landscape near the Bolivian border. The El Tatio geyser field, located at 4320 meters elevation 90 kilometers north of San Pedro de Atacama, contains approximately 80 active geysers that reach maximum activity between 6:00 and 7:00 AM local time when thermal differential between groundwater and air temperature peaks. Air temperatures at El Tatio commonly drop to minus 20°C before dawn while geyser water emerges at 86°C, creating steam columns visible up to two kilometers distant.
The semiarid Norte Chico region extends from approximately 27 to 32 degrees south latitude, encompassing La Serena and Coquimbo. Average annual rainfall increases from 25 millimeters at Copiapó to 130 millimeters at La Serena, concentrated almost entirely between May and August. This region experiences sporadic "flowering desert" events when El Niño conditions deliver rainfall exceeding 30 millimeters between June and September, triggering mass germination of dormant seeds. The most extensive documented flowering occurred in 2015 when 60 millimeters fell between March and May, creating floral coverage across an estimated 20,000 square kilometers. Pan de Azúcar National Park, where the coastal range meets the Pacific at 26 degrees south latitude, demonstrates the transition zone where coastal fog (camanchaca) provides sufficient moisture for scattered vegetation despite annual rainfall below 15 millimeters.
Central Chile, extending from approximately 32 to 37 degrees south latitude, contains 65 percent of the nation's population within a climate classified as Mediterranean (Köppen Csb/Csa). Santiago, at 570 meters elevation in the Central Valley, receives 312 millimeters of precipitation annually with 78 percent falling between May and August. January average maximum temperatures in Santiago reach 29.4°C while July minimums average 3.7°C based on Dirección Meteorológica de Chile data from 1981 to 2010. The Central Valley averages 50 kilometers in width between the Coastal Range (averaging 2000 meters elevation) and the Andes (averaging 5000 meters in this latitude). Aconcagua (6961 meters), the Western Hemisphere's highest peak, lies just across the Argentine border 112 kilometers northeast of Santiago, visible from the capital on clear days. Winter snow accumulation in the Andes above 2500 meters elevation feeds rivers including the Maipo, Maule, and Biobío, which provide 70 percent of Santiago's water supply and 55 percent of Chile's hydroelectric generation capacity.
Valparaíso, located on the Pacific coast 112 kilometers northwest of Santiago, experiences more moderate temperatures due to oceanic influence, with January maximums averaging 22.9°C and July minimums averaging 8.8°C. Annual precipitation in Valparaíso measures 415 millimeters, 33 percent higher than Santiago despite proximity, due to orographic lift from 42 cerros (hills) within the urban area reaching elevations up to 510 meters. The Humboldt Current maintains Pacific Ocean surface temperatures off Valparaíso between 12°C in August and 17°C in February, approximately 5 to 8 degrees below temperatures typical for this latitude without cold current influence. This current carries nutrient-rich water northward from Antarctic regions, supporting one of the world's most productive marine ecosystems with anchovy densities documented at 35 kilograms per cubic meter during peak seasonal concentrations.
The Lake District (Región de Los Lagos and Región de Los Ríos) extends from approximately 37 to 43 degrees south latitude, characterized by temperate oceanic climate (Köppen Cfb) with year-round precipitation. Valdivia, at 5 meters elevation, receives 2593 millimeters of precipitation annually distributed relatively evenly across all months, though winter months from May to August average 280 millimeters monthly compared to 120 millimeters in December and January. Temperature ranges narrow significantly compared to Santiago, with Valdivia's January maximums averaging 23.4°C and July minimums averaging 4.6°C. This region contains twelve major lakes formed by glacial activity during the last ice age, which peaked approximately 18,000 years before present. Lake Llanquihue, covering 860 square kilometers at 51 meters elevation, ranks as South America's second-largest lake entirely within one country. Osorno volcano (2652 meters) and Calbuco volcano (2003 meters) dominate Llanquihue's eastern shore, both classified as active with Calbuco's most recent eruption occurring in April 2015.
Chiloé Island, separated from mainland Chile by the Chacao Channel (2.5 kilometers wide at its narrowest point), measures 180 kilometers north to south and covers 8394 square kilometers, making it South America's second-largest island after Tierra del Fuego. Chiloé receives between 2000 and 2500 millimeters of precipitation annually with persistent cloud cover year-round. The island's western coast faces the Pacific with essentially no land mass interruption until Antarctica, generating powerful oceanic swells that historically isolated western Chiloé communities. Native Valdivian temperate rainforest covers approximately 40 percent of Chiloé, dominated by species including coigüe, canelo, and arrayán. This forest type once extended along Chile's coast from 37 to 48 degrees south latitude but now survives in fragmented sections totaling approximately 248,000 square kilometers across Chile and Argentina.