Terms starting with M

MAP

Graphic representation of the physical features (natural, artificial, or both) of a part or the whole of the Earth's surface, by means of signs and symbols or photographic imagery, at an established scale, on a specified projection, and with the means of orientation indicated.

  • Map, Base: Map on which information may be placed for purposes of comparison or geographical correlation. The term "base map" was at one time applied to a class of maps now known as outline maps. It may be applied to topographic maps, also termed "mother maps" that are used in the construction of other types of maps by the addition of particular data.

  • Map, Bathymetric: Maps delineating the form of the bottom of a body of water, or a portion thereof, by the use of depth contours (isobaths)

  • Map, Cadastral: Map showing the boundaries of subdivisions of land, often with the bearings and lengths thereof and the areas of individual tracts, for purposes of describing and recording ownership. It may also show culture, drainage, and other features relating to land use and value.

  • Map, Choropleth: Thematic map in which areas are colored, shaded, dotted, or hatched to create darker or lighter areas in proportion to the density of distribution of the theme subject. 

MAP DIGITIZATION

Conversion of map data from graphic to digital form.

  • Map, Engineering: Map showing information that is essential for planning an engineering project or development and for estimating its cost. It usually is a large-scale map of a small area or of a route. It may be entirely the product of an engineering survey, or reliable information may be collected from various sources for the purpose, and assembled on a base map.

  • Map, Flood Control: Map designed for studying and planning control projects in areas subject to flooding.

  • Map, Forestry: Map prepared principally to show the size, density, kind, and value of trees in a designated area.

  • Map, Geologic: Map showing the structure and composition of geologic features.

  • Map, Land use: Map showing by means of a coding system the various purposes for which parcels of land are being used by man.

  • Map, Line: Map composed of lines as distinguished from photographic imagery.

  • Map, Planimetric: Map that presents only the horizontal positions for features represented. distinguished from a topographic map by the omission of relief in measurable form. The features usually shown on a planimetric map include rivers, lakes, and seas; mountains, valleys, and plains; forests, and prairies; cities, farms transportation routes, and public utility facilities; and political and private boundary lines. A planimetric map intended for special use may present only those features essential to the purpose to be served. 

MAP PROJECTIONS

Map projections flatten a curved Earth surface, which naturally distorts distance information away from the center of the flattened area. As a result, particular projections were developed for certain areas. Using an improper projection can create large distortions. For example, distortion is clearly visible with a UTM projection (which is one of the most common) of Antarctica, where Antarctica seems as large as Asia and North America combined. Because the most accurate portion of a UTM is at the center of the map, that would be the least distorted area represented.

For example, knowing the correct map projection should prevent you from using UTM to produce an image map of Antarctica; instead, use the projection developed for that area, Polar Stereographic. Since maps represent distance, it is important to choose the same map projection for data layers that are overlaid on an image.

 The following are the most common map projection:

Abbreviation    

Full Name

UTM

Universal Trans Mercator

PS

Polar Stereographic

SOM

Standard Oblique Mercator

ACEA

Albers Conical Equal Area

AE

Azimuthal Equidistant

EC

Equidistant Conic Types A/B

ER

Equirectangular/Platte Carree

GK

Gauss-Krueger

GVNP

General Vertical Near side perspective

GNO

Gnomonic

LAEA

Lambert Azimuthal Equal Area

LCC

Lambert Conformal Conic

MER

Mercator

MC

Miller Cylindrical

OM

Oblique Mercator

OG

Orthographic

PC

Polyconic

SIN

Sinusoidal

SPCS

State Plane Coordinate System

SG

Stereographic

TM

Transmercator

VDG

Van Der Grinten

MAP SERIES

Family of maps conforming generally to the same specifications and designed to cover an area or a country in systematic pattern.

  • Map, Slope (clinometric map): Map showing the degree of steepness of the Earth's surface by the use of various colors or shading for critical ranges of slope.

  • Map, Soil: Map that shows the constitution, structure, and texture of the soil and identifies ongoing erosion.

  • Map, Storm Evacuation: Map designed to identify coastal areas subject to flooding, to indicate recommended areas of refuge, and to emphasize available evacuation routes.

  • Map, Thematic: Map designed to provide information on a single topic, such as geology, rainfall, population.

  • Map, Topographic: Map that present the horizontal and vertical positions of the features represented; distinguished from a planimetric map by the addition of relief in measurable form.

MARSH, COASTAL

Area of salt-tolerant vegetation in brackish and (or) saline-water habitants subject to tidal inundation.

MARSH, FRESHWATER

Tract of low wet ground, usually miry and covered with rank vegetation.

MEAN HIGH WATER

Tidal datum that is the arithmetic mean of the high water heights observed over a specific 19-year Metonic cycle (National Tidal Datum Epoch). For stations with shorter series, simultaneous observations are made with a primary control tide station to derive the equivalent of a 19-year value. Use of "mean high tide" is discouraged.

Mean High Water Line: Intersection of the land with the water surface at the elevation of high water.

MEAN LOW WATER

Tidal datum that is the arithmetic mean of the low water heights observed over a specific 19-year Metonic cycle (National Tidal Datum Epoch). For stations with shorter series, simultaneous observations are made with a primary control tide station to derive the equivalent of a 19-year value. Use of "mean low tide" is discouraged.

Mean Low Water Line: Intersection of the land with the water surface at the elevation of low water. 

MEAN SEA LEVEL

Tidal datum that is the arithmetic mean of the hourly water elevations observed over a specific 19-year Metonic cycle (National Tidal Datum Epoch). Shorter series are specified in the name; that is, monthly mean sea level and yearly mean sea level.

MEANDER LINE

Metes-and-bounds traverse approximately along the mean high water line of a permanent body of water. By following the sinuosities of the bank or shoreline, the meander line provides data for computing the area of land remaining after the water area has been segregated. A meander line differs from other metes and bounds surveys in that it does not ordinarily determine or fix boundaries.

MERIDIAN

Great circle on the surface of the Earth passing through the geographical poles and any given point on the Earth's surface. All points on a given meridian have the same longitude.

METADATA

For formats other than NITF, the metadata is supplied as separate files on the delivered media. The metadata contains the information needed to ingest the image/data into a GIS software. If there are problems reading the imagery, the solution may lie in the metadata.

METES AND BOUNDS

Method of describing land by measure of length (metes) of the boundary lines (bounds).

METONIC CYCLE

Period of 235 lunations or about 19 years. devised by Meton, an Athenian astronomer (5th century B.C.) for the purpose of obtaining a period at the end of which the phases of the moon recur in the same order and on the same days as in the preceding cycle.

METRIC SYSTEM

Decimal system of weights and measures based on the meter as a unit length and the kilogram as a unit mass.