Map Terms





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Altitude of a point is defined as the distance either above or below a reference point.

All altitude measurements below the reference should be designated by a minus sign (-) preceding the number.  Measurements at or above the reference may be either without a sign or may be designated by a plus sign (+).


To furnish with critical commentary or notes.


A book or bound collection of maps, sometimes with supplementary illustrations and graphic analyses.


The art or technique of making maps or charts. A cartographer is a person who makes maps.



The Curvimeter is an instrument used to measures straight and curved lines by hand. Measurement of angles, maps and drawings is made easy.



Having a shared boundary; being immediately adjacent. Example: contiguous United States; states physically located next to one another.


Contour is the name given to a line drawn to represent connecting points of equal height.   When referring to maps, a contour refers to a 'contour line' drawn on a map to represent an imaginary line on the ground, with all its points being at the same elevation above or below a specified datum; usually 'mean sea level'.

Contour lines help the map user, to visualize the lay of the land.


A coordinate is a set of numbers that describe a precise position. A precise position along a line, on a surface, or, in space, is measured, described and referenced in the form of a coordinate.


Coordinates refers to a set of numbers that describe precise positions; along a line, on a surface, or, in space.

Latitude and longitude, or declination and right ascension, each are a system of coordinates on the surface of a sphere; on the globe of the Earth; or, the globe of the heavens.

Map Coordinates

UTM Coordinates, Cartesian Coordinates are examples of flat grid systems used on maps.

Cartesian coordinates are sometimes used on maps, but most commonly used on graphs.  The Cartesian coordinate system is based on a set of axes perpendicular to each other.  The system is based on two straight lines ("axes"), perpendicular to each other, each of them marked with the distances from the point where they meet ("origin").  Distances to the right and above the "origin point, represents positive values; and the opposite sides as negative values.

Cartesian Coordinate Graphic Demonstration  (link off site, at Oswego City School District web site)

Another Fun Cartesian Coordinate Online Practice - Refresh Your Skill Set!

3 Dimension Cartesian Coordinates

The two Cartesian axes (x,y) can be extended to 3 dimensions by adding a third coordinate.  This third coordinate defines height when working with maps and space, as is labeled and referred to as 'z'.  The third dimension is perpendicular to the flat plane described by x and y.

Alt-Azimuth Coordinates

The alt-azimuth (altitude - azimuth) coordinate system, also called the horizon system, is a useful and convenient system for pointing out a celestial object.


A datum is a set of constants, specifying the coronate system used for geodetic referencing, i.e., for calculating coordinates of points on the Earth. ( Ref. the NGS (National Geodetic Survey).

Specific geodetic datums are usually given distinctive names.

In other words, a datum is a set of parameters and reference points used to mathematically define the three-dimensional shape of the Earth (e.g., as a spheroid).

For example, the "North American Datum for 1983" (NAD83) is the datum for map projections and coordinates within the United States and throughout North America.


Declination is the error between "true North" (North Pole) and magnetic North. All maps are based on true North; and all magnetic compass needles point to magnetic North.

See Current Magnetic Declination In USA

Declination Angle

The declination angle is the measure of angle between the bearings of true North and magnetic North. The declination angle is different all over the world. In the United States it varies by as much as 42 degrees from coast to coast.

See Map Glossary For Current Magnetic Declination Data


Digital Raster Graphics

A digital raster graphic (DRG) is a scanned image of a U.S. Geological Survey (USGS) standard series topographic map, including all map collar information. The image inside the map neatline is georeferenced to the surface of the earth and fit to the Universal Transverse Mercator projection. The horizontal positional accuracy and datum of the DRG matches the accuracy and datum of the source map. The map is scanned at a minimum resolution of 250 dots per inch.  (Reference: U.S.G.S Definition.)

DXF Format

Drawing Interface Format. An AC\SCII file format used by various graphic and CAD programs. Each ASCII line in a DXF file describes an object within the overall drawing.


A geographic dictionary or index. U.S. Gazetteer

Geodetic Datums

See Datum

Geographic Coordinates

Geographic coordinates reference precision points on the surface of a  planet.

Earth's Geographic Coordinate System

The North and South poles are defined by the Earth's axis of rotation; equidistant between them is the equator.  North-south latitude is measured in degrees from the equator, ranging from -90 degrees at the south pole, 0 degrees at the equator, to +90 degrees at the north pole.  East-west distances are also measured in degrees, but there is no "naturally-defined" starting point; all longitudes are equivalent to all others.

It has become a internationally excepted standard to arbitrarily define the 'prime meridian' (0 degrees longitude) to be at the Royal Observatory at Greenwich, England; alternately called the Greenwich meridian.

Each degree of a 360 degree circle can be further subdivided into 60 equal minutes of arc ('), and each arc-minute may be divided into 60 seconds of arc (").

Example Coordinate

The 24-inch telescope at Sommers-Bausch Observatory is located at a latitude of 40 d 0'13" North of the equator and at a longitude 105 d 15'45" West of the Greenwich meridian.

Geospatial Sciences Division

A Division of the National Imagery and Mapping Agency

Satellite Geodesy - GPS Data, Control Data

Physical Geodesy - WGS 84 - Grids & Projections

Geodetic Surveying



Geographic Information Systems

GIS can be used in a variety of technology fields such as engineering, resource management, public utility management, business, town planning, etc..


A grid of lines that display meridians of longitude and parallels of latitude.

Greenwich Meridian

It has become a internationally excepted standard to arbitrarily define the 'prime meridian' (0 degrees longitude) to be at the Royal Observatory at Greenwich, England; alternately called the Greenwich meridian.

Hydrographic Charts

Hydrographic charts are maps that represent the surface and shores of large bodies of water on earth. Ships navigate by using hydrographic charts.

Improving Positional Accuracy

NSG Online Data


Intertidal is the name given to an area of land that is exposed during low tide conditions and covered during high tide conditions along a coast line.  Another name for this area is the "littoral" zone.


The angular distance of a point on the earth's surface along a meridian north or south of the equator.


The angular distance of a point on the earth's surface east or west of an arbitrarily defined meridian, usually the Greenwich meridian (Greenwich, England).


A map is a drawn or printed representation of something.  Maps of the earth, are a scaled representation of features on earth drawn or printed on a flat surface. See Types of Maps.

Map Coordinate

A map coordinate is a set of values, which describes a precise point on a map.

Map Coordinates

Map coordinates are sets of values, which describe precise points on a map.

Map Scale

The proportion between a unit of length on a map and the same length in reality (the real world), is the "scale" of a map.  Selecting the appropriate map scale depends on the intended application and use of the map (Topo Map, Street Map, Roadway Map, Road Atlas, Marine Chart, Lake Map, Fishing Map, Mineral Deposits, Tourist Map, etc..).  For More Information Go To These Pages:

Map Scale   Map Scales   Which Map Scale Is Best?

Magnetic Declination In U.S.A.

Compute Values of Earth's Magnetic Field (Version 4.0) - Online Calculator provided by NOAA web site. Click Here

This form computes the estimated values of Earth's magnetic field, including magnetic declination (D), based on the current International Geomagnetic Reference Field (IGRF).


"Neatline" Is The Word Given To A Border-Line Commonly Drawn Around A Map's Actual Plotted Reference Area Image; Defining The Edge Of The Plotted Area And The Map's Margin; Also Called A Map-Collar, Where The Map's Reference Notes, Scale, Grid Tics, And Other Important Map Information, Are Printed.


National Imagery and Mapping Agency



National Geodetic Survey

NGS Emblem



National Oceanic and Atmospheric Administration




A mathematical technique that converts and portrays features from a spherical surface onto a 2-D plane.

Spatial Address

Spatial address refers to the geographic point location of an object, and is used to define the position of a point (in a defined coordinate system) that may be on, above, or below the Earth's surface.


A set of software application programs integrated together as a working platform on a desktop or laptop computer.   A map application suite is a computer based working environment for working with map images.  Professional grade and navigation grade map software suites will come with a statement of accuracy for map creation, measurement or navigation.  Suites may include: maps  to scale, along with a collection of map tools such as; map-image importing and exporting tool, map-image calibration for working to precise scale on the PC screen, measurement tools, tools for drawing on map images, tools for creating waypoints and routes used by GPS systems, map printing tools and more.

Tiger Map


U.S. Census Bureau Tiger Map Surfer and Gazetteer

Picture of the Census Bureau TIGER.


Topographic Map

Topographical Map

A graphic representation of land contour and surface-features, mapped to a scale of measure, indicating relative positions and elevations.

A topographical map is a drawing that represents the lands natural features and some notable human-made features. A topographical map may also include political boundaries.

A map is a representation of the Earth, or part of it.  The distinctive characteristic of a topographic map is that the shape of the Earth's surface is shown by contour lines.  Contours are imaginary lines that join points of equal elevation on the surface of the land above or below a reference surface, such as mean sea level. Contours make it possible to measure the height of mountains, depths of the ocean bottom, and steepness of slopes directly from a topographic map.

USGS QUAD MAP TOOL  Measure Slope Angles Directly FromTopographical Maps

Topographic map shows more than contours.  The map includes symbols that represent such features as streets, buildings, streams, and vegetation.  These symbols are constantly refined to better relate to the features they represent, improve the appearance or readability of the map, or reduce production cost.

Consequently, within the same series, maps may have slightly different symbols for the same feature. Examples of symbols that have changed include built-up areas, roads, intermittent drainage, and some lettering styles. On one type of large-scale topographic map, called provisional, some symbols and lettering are hand drawn.

Each Government Will Have Their Own Set Of Map Symbols And Definitions Used On Their Topographical Maps.

  A current Topographical Map is now used when working with UTM coordinates

Topographical maps are now the standard map to use when working with the internationally universal UTM world coordinate grid system.  Quickly pinpoint and plot any point on the earth's surface with a unique two number address.

USGS TOPO QUAD TOOL Measures Slope Angles Directly From A USGS Quad 7.5 Minute Topographical Map And Many Other Topographical Map Measuring And Plotting Tasks.

Topo Map

"TOPO Map" stands for "Topographical Map"

Types of Maps

A topographical map is a drawing that represents the lands natural features and some notable human-made features. A topographical map may also include political boundaries.

Hydrographic charts are maps that represent the surface and shores of large bodies of water on earth. Ships navigate by using hydrographic charts.

Some other special-purpose maps include political maps, which show only political divisions without topographic features of the land; geologic maps, which represent the geologic structure of a specific area of land; and maps indicating social and scientific data.


Universal Polar Stereographic

The Universal Polar Stereographic Grid System (UPS) is used in place of UTM in the polar regions of greater than 84 degrees north latitude and 80 degrees south latitude.  Characteristics of UTM (paragraph C.2.1) also apply to UPS, with some important modifications.  The 0 degree and 180 degree meridians divides each polar region into an eastern and western half.  At the north pole, the western grid zone is labeled "Y" and the eastern grid zone "Z".  The corresponding south polar grid zones are labeled "A" and "B".  The location of any point within either of the polar regions is given in relation to the 180 degree meridian and 90 degree meridian.  A value of 2,000,000 meters north and 2,000,000 meters east is added in order to avoid negative numbers.

Universal Transverse Mercator (UTM)c

Universal Transverse Mercator.  UTM is a popular coordinate system used in survey and mapping applications. UTM relies on grid zone designations, easting/northing distances and provides one meter resolution.

The Universal Transverse Mercator Grid System (UTM) provides rectangular coordinates that may be used to indicate locations of points on the surface of the Earth.  UTM involves linear measurements, and the unit of measure is the meter.  A point is located by specifying a hemispheric-indicator, a zone-number, an easting value, and a northing value.

More About UTM

How To Use UTM

How To Read UTM Coordinates

How To Plot A UTM Coordinate On A Map


United States Geological Survey (USGS)

Created by an act of Congress in 1879, the USGS has evolved over 125 years, matching its talent and knowledge to the progress of science and technology.  Today, the USGS stands as the sole science agency for the Department of the Interior of the United States.  It is sought out by thousands of partners and customers for its natural science expertise and its vast earth and biological data holdings.  The USGS is the science provider of choice in accessing the information and understanding to help resolve complex natural resource problems across the Nation and around the world.


Universal Transverse Mercator / Universal Polar Stereographic

The Abbreviation Stands For "Universal Transverse Mercator/Universal Polar Stereographic Grid Systems".

Vertical Datums, Elevations, and Heights

The zero surface to which elevations or heights are referred is called a vertical datum.

Traditionally, surveyors and mapmakers have tried to simplify the task by using the average (or mean) sea level as the definition of zero elevation, because the sea surface is available worldwide.


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