41°53′11″N 87°38′15″W / 41.88639°N 87.63750°W
The Chicago River is a system of rivers and canals with a combined length of 156 miles (251 km) that runs through the city of Chicago, including its center (the Chicago Loop). The river is one of the reasons for Chicago's geographic importance: the related Chicago Portage is a link between the Great Lakes and the Mississippi River Basin, and ultimately the Gulf of Mexico.
The Loop is Chicago's central business district and one of the city's 77 municipally recognized community areas. Located at the center of downtown Chicago on the shores of Lake Michigan, it is the second-largest business district in North America, after Midtown Manhattan in New York City. It contains the world headquarters and regional offices of several global and national businesses, retail establishments, restaurants, hotels, museums, theaters, and libraries—as well as many of Chicago's most famous attractions. The district also hosts Chicago's City Hall, the seat of Cook County, offices of the state of Illinois, United States federal offices, and several foreign consulates. The intersection of State Street and Madison Street in the Loop is the origin point for the address system on Chicago's street grid, a grid system that has been adopted by numerous cities worldwide.
The Loop's definition and perceived boundaries have evolved over time. Since the 1920s, the area bounded by the Chicago River to the west and north, Lake Michigan to the east, and Roosevelt Road to the south has been called the Loop. It took its name from a somewhat smaller area, the 35 city blocks bounded on the north by Lake Street, on the west by Wells Street, on the south by Van Buren Street, and on the east by Wabash Avenue—the Union Loop formed by the 'L' in the late 1800s. Similarly, the "South Loop" and the "West Loop" historically referred to areas within the Loop proper, but in the 21st century began to refer to the entire Near South and much of the Near West Sides of the city, respectively.
The Illinois Waterway system consists of 336 miles (541 km) of navigable water from the mouth of the Calumet River at Chicago to the mouth of the Illinois River at Grafton, Illinois. Based primarily on the Illinois River, it is a system of rivers, lakes, and canals that provide a commercial shipping connection from the Great Lakes to the Gulf of Mexico via the Illinois and Mississippi rivers.
The Illinois and Michigan Canal (I&M) opened in 1848. In 1900, the Chicago Sanitary and Ship Canal replaced the I&M and reversed the flow of the Chicago River so it no longer flowed into Lake Michigan. The United States Army Corps of Engineers maintains a 9-foot-deep (2.7 m) navigation channel in the waterway. The waterway's complex northern section is referred to in various contexts for study and management as the Chicago Area Waterway System (CAWS).
A flow tracer is any fluid property used to track the flow velocity (i.e., flow magnitude and direction) and circulation patterns. Tracers can be chemical properties, such as radioactive material, or chemical compounds, physical properties, such as density, temperature, salinity, or dyes, and can be natural or artificially induced. Flow tracers are used in many fields, such as physics, hydrology, limnology, oceanography, environmental studies and atmospheric studies.
Conservative tracers remain constant following fluid parcels, whereas reactive tracers (such as compounds undergoing a mutual chemical reaction) grow or decay with time. Active tracers dynamically alter the flow of the fluid by changing fluid properties which appear in the equation of motion such as density or viscosity, while passive tracers have no influence on flow.
The Great Chicago Fire was a conflagration that burned in the American city of Chicago, Illinois, during October 8–10, 1871. The fire killed approximately 300 people, destroyed roughly 3.3 square miles (9 km) of the city including over 17,000 structures, and left more than 100,000 residents homeless. The fire began in a neighborhood southwest of the city center. A long period of hot, dry, windy conditions, and the wooden construction prevalent in the city, led to the conflagration spreading quickly. The fire leapt the south branch of the Chicago River and destroyed much of central Chicago and then crossed the main stem of the river, consuming the Near North Side.
Help flowed to the city from near and far after the fire. The city government improved building codes to stop the rapid spread of future fires and rebuilt rapidly to those higher standards. A donation from the United Kingdom spurred the establishment of the Chicago Public Library.
The Illinois and Michigan Canal connected the Great Lakes to the Mississippi River. In Illinois, it ran 96 miles (154 km) from the Chicago River in Bridgeport, Chicago to the Illinois River at LaSalle-Peru. The canal crossed the Chicago Portage, and helped establish Chicago as the transportation hub of the United States, before the railroad era. It was opened in 1848. Its function was partially replaced by the wider and deeper Chicago Sanitary and Ship Canal in 1900, and it ceased transportation operations with the completion of the Illinois Waterway in 1933.
Illinois and Michigan Canal Locks and Towpath, a collection of eight engineering structures and segments of the canal between Lockport and LaSalle-Peru, was designated a National Historic Landmark in 1964.
The city of Chicago is divided into 77 community areas for statistical and planning purposes. Census data and other statistics are tied to the areas, which serve as the basis for a variety of urban planning initiatives on both the local and regional levels. The areas' boundaries do not generally change, allowing comparisons of statistics across time. The areas are distinct from but related to the more numerous neighborhoods of Chicago; an area often corresponds to a neighborhood or encompasses several neighborhoods, but the areas do not always correspond to popular conceptions of the neighborhoods due to a number of factors including historical evolution and choices made by the creators of the areas. As of 2020, Near North Side is the most populous of the areas with over 105,000 residents, while Burnside is the least populous with just over 2,500. Other geographical divisions of Chicago exist, such as the "sides" with origin in the 3 branches of the Chicago River, the 50 wards of the Chicago City Council which undergo redistricting based in population movements, and the parishes of the Roman Catholic Church.
The Social Science Research Committee at the University of Chicago defined the community areas in the 1920s based on neighborhoods or groups of related neighborhoods within the city. In this effort it was led by sociologists Robert E. Park and Ernest Burgess, who believed that physical contingencies created areas that would inevitably form a common identity. Except for the addition of two areas (O'Hare from land annexed by the city in 1956 and Edgewater's separation from Uptown in 1980) and peripheral expansions due to minor annexations, the areas' boundaries have never been revised to reflect change but instead have been kept stable. The areas have become a part of the culture of Chicago, contributing to its perception as a "city of neighborhoods" and breaking it down into smaller regions for easier analysis and local planning. Nevertheless, Park's and Burgess's ideas on the inevitability of physically related areas forming a common bond have been questioned, and the unchanging nature of the areas has at times been seen as analytically problematic with major subsequent changes in some of the areas' urban landscapes, such as the construction of expressways.
State Street is a large south-north street, also one of the main streets, in Chicago, Illinois, United States and its south suburbs. Its intersection with Madison Street (41°52′55″N 87°37′40″W / 41.8820°N 87.6278°W) has marked the origin for Chicago's address system since 1909. State begins in the north at North Avenue, the south end of Lincoln Park, runs south through the heart of the Chicago Loop, and ends at the southern city limits, intersecting 127th Street along the bank of the Little Calumet River. It resumes north of 137th Street in Riverdale and runs south intermittently through Chicago's south suburbs until terminating at New Monee Road in Crete, Illinois.
From north to south, State Street traverses the following community areas of Chicago: Near North Side to the Chicago River, Chicago Loop to Roosevelt Road, Near South Side to 26th Street, Douglas to 39th Street, Grand Boulevard to 51st Street, Washington Park to 63rd Street, Grand Crossing to 79th Street, Chatham to 91st Street, Roseland to 115th Street, and West Pullman to 127th Street, where it terminates across from Riverdale Bend Woods. The street runs parallel and adjacent to the Dan Ryan Expressway from 65th Street south to just beyond 95th Street, where State Street crosses the I-94 Bishop Ford Memorial Freeway to enter Roseland.
Madison Street is a major east–west street in Chicago, Illinois. Prior to human intervention, in the early 19th century the Chicago River after forming a large bend emptied into Lake Michigan at the present day intersection of Madison Street and Michigan Avenue. The street in the central was laid out in the first plat of Chicago.
Notable buildings located along Madison Street include the Carson, Pirie, Scott and Company Building, Chase Tower, Three First National Plaza, the Chicago Civic Opera House, Citigroup Center and the United Center. The West Side's United Center is across Madison Street from the former site of the Chicago Stadium, "the Madhouse on Madison" (demolished in 1995).