A map is a symbolic representation of selected characteristics of a place, usually drawn on a flat surface. Maps present information about the world in a simple, visual way. They teach about the world by showing sizes and shapes of countries, locations of features, and distances between places. Maps can show distributions of things over the Earth, such as settlement patterns, and exact locations of houses and streets in a neighborhood.
Cartographers create maps for many different purposes. Hikers, backpackers, and hunters consult topographic maps to plot routes for their trips. Family historians and genealogists use Sanborn fire insurance maps, originally created for fire insurance purposes, to research family background and ancestry. City planners decide where to put hospitals and parks with the help of maps that show land features and how the land is currently being used. Some common features of maps include scale, symbols, and grids. source: National Geographic Resource Library, Encyclopedic Entry: Map.
Cartographers make many different types of maps, which can be divided into two broad categories: general reference and thematic.
These maps show general geographic information about an area, including the locations of cities, boundaries, roads, mountains, rivers, and coastlines. Government agencies such as the U.S. Geological Survey (USGS) make some general reference maps. Many are topographic maps, meaning that they show changes in elevation. They show all the hills and valleys in an area. This is useful to everyone from hikers trying to choose a route to engineers trying to determine where to build highways and dams.
These maps display distributions, or patterns, over Earth’s surface. They emphasize one theme, or topic. These themes can include information about people, other organisms, or the land. Examples include crop production, people’s average income, or where different languages are spoken.
Sanborn maps were created to assist fire insurance companies as they assessed the risk associated with insuring a particular property. They show information such as the outline of each building, the size, shape and construction materials, heights, and function of structures.
Many thematic maps are now made with the help of geographic information system (GIS) technology. GIS are computer systems that capture, store, and display data related to positions on Earth’s surface. This technology combines information from maps with other data about people, the land, climate, farms, houses, businesses, and much more, allowing multiple sets of data to be displayed on a single map. Many industries and governments use GIS technology for analysis and decision making. For example, GIS data helps officials determine which streams are most in danger of being polluted. It can also help a business decide where to locate a new store.
The distinctive characteristic of a topographic map is the use of elevation contour lines to show the shape of the Earth's surface. Elevation contours are imaginary lines connecting points having the same elevation on the surface of the land above or below a reference surface, which is usually mean sea level. Contours make it possible to show the height and shape of mountains, the depths of the ocean bottom, and the steepness of slopes.
Longitude is the imaginary (but very important) lines that run from the North Pole to the South Pole. Each is identified by the number of degrees it lies east or west of the so-called prime meridian in Greenwich, England (part of London).
NASA provides an explanation of latitude and longitude with diagrams.
Scale is defined as the ratio of the distance on the map to the distance on the ground.
For more information, see the USGS Fact Sheet on Map Scales.
Cartographers use symbols to represent geographic features. For example, black dots represent cities, circled stars represent capital cities, and different sorts of lines represent boundaries, roads, highways, and rivers. Colors are often used as symbols. Green is often used for forest, tan for deserts, and blue for water. A map usually has a legend, or key, that gives the scale of the map and explains what the various symbols represent. source: National Geographic Resource Library, Encyclopedic Entry: Map.
Many maps include a grid pattern, or a series of crossing lines that create squares or rectangles. The grid helps people locate places on the map. On small-scale maps, the grid is often made up of latitude and longitude lines. Latitude lines run east-west around the globe, parallel to the Equator, an imaginary line that circles the middle of the Earth. Longitude lines run north-south, from pole to pole. Latitude and longitude lines are numbered. The intersection of latitude and longitude lines, called coordinates, identify the exact location of a place. source: National Geographic Resource Library, Encyclopedic Entry: Map.
Township and Range
Originally proposed by Thomas Jefferson, the PLSS began shortly after the Revolutionary War, when the federal government became responsible for large areas west of the thirteen original colonies. The Land Ordinance of 1785 which provided for the systematic survey and monumentation of public domain lands, and the Northwest Ordinance of 1787 which established a rectangular survey system designed to facilitate the transfer of federal lands to private citizens, were the beginning of the PLSS. Under Congressional mandate, cadastral surveys (surveys of the boundaries of land parcels) of public lands were undertaken to create parcels suitable for disposal by the Government. The Manual of Instructions for the Survey of the Public Lands Of The United States, 2009 documents current official procedures for PLSS surveys.
To learn more, access the Public Land Survey System article published by the USGS, from which this information was sourced.
The phrase "USGS topographic map" can refer to maps with a wide range of scales, but the scale used for all modern USGS topographic maps is 1:24,000. That covers a quadrangle that measures 7.5 minutes of longitude and latitude on all sides, so these are also referred to as 7.5-minute maps, quadrangle maps, or “quad” maps (modern topographic maps for Alaska have a scale of 1:25,000 and cover a variable distance of longitude). Each topographic map has a unique name.
Degrees, Minutes, or Seconds
The distances vary. A degree, minute or second of latitude remains fairly constant from the equator to the poles; however a degree, minute, or second of longitude can vary greatly as one approaches the poles (because of the convergence of the meridians). At 38 degrees North latitude, one degree of latitude equals approximately 364,000 ft (69 miles), one minute equals 6068 ft (1.15 miles), one-second equals 101 ft; one-degree of longitude equals 288,200 ft (54.6 miles), one minute equals 4800 ft (0.91 mile), and one second equals 80 ft.
The Federal Communications Commissions provides this online degrees, minutes, seconds converter.
An atlas is a book or collection of maps. Many atlases also contain facts and history about certain places. There are many kinds of specialized atlases, such as road atlases and historical atlases. There are also star atlases, which give the location and placement of stars, planets and other celestial objects. source: National Geographic Resource Library, Encyclopedic Entry: Atlas
A spherical representation of the earth with its map on the surface, especially one which is fixed to a stand and may be rotated on a vertical (or near-vertical) axis (more fully a terrestrial globe); a similar representation of the stars and constellations. source: Oxford English Dictionary