Maps Glossary

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A maar is a type of volcanic crater that is formed when hot magma comes in contact with water, causing a steam explosion.  The resulting crater is generally broad and shallow, with a low rim that often contains water.  Maars can be found all over the world, and are typically surrounded by a ring of tuff deposits.

Magnetic Declination

Magnetic declination refers to the angle between magnetic north and true north, and is caused by variations in the Earth’s magnetic field.  The value of magnetic declination changes depending on where you are in the world, and can be determined by using a compass or by consulting a map with declination information.

Magnetic North

Magnetic north is the direction that a compass needle points towards, which is caused by the Earth’s magnetic field.  Unlike true north, which is the geographic North Pole, magnetic north is not fixed and can change over time due to variations in the Earth’s magnetic field.

Magnetic Variation

Magnetic variation, also known as magnetic deviation, is the difference between magnetic north and true north at a particular location on the Earth’s surface.  It is caused by the fact that the Earth’s magnetic field is not perfectly aligned with the planet’s rotational axis. Magnetic variation can be positive or negative, and is measured in degrees.  It is important for navigation, as it can affect the accuracy of compass readings.


In geology, magnitude refers to the measure of the strength or size of an earthquake.  It is typically measured using the Richter scale or the moment magnitude scale, both of which use seismographic readings to determine the amount of energy released during an earthquake.  The higher the magnitude, the more severe the earthquake.

Mainline Control

Mainline control refers to the process of establishing a set of guidelines and procedures for the construction and maintenance of a pipeline or other linear infrastructure project.  This involves developing safety protocols, identifying potential hazards and risks, and ensuring compliance with environmental regulations.  Mainline control is essential for preventing accidents and protecting both people and the environment.

Major Fault

A major fault is a large fracture in the Earth’s crust along which there has been significant movement. Faults are formed by tectonic forces and can be found all over the world.  Major faults are those that have caused significant earthquakes or have displaced large areas of land.  They can be thousands of kilometers long and extend several kilometers deep into the Earth’s crust.


The mantle is the layer of the Earth that lies between the crust and the core. It is composed of hot, dense rock that is in a constant state of motion due to the heat generated by the Earth’s core.  The mantle plays a critical role in the formation of tectonic plates and the movement of the Earth’s crust, which can cause earthquakes and volcanic activity.


A map is a two-dimensional representation of a three-dimensional space, typically used to convey geographical information.  Maps can show a wide range of features, including terrain, bodies of water, roads, and political boundaries.  They are used for a variety of purposes, from navigation to urban planning to scientific research.

Map Accuracy

Map accuracy refers to the degree to which a map represents the actual features of the landscape it depicts. Accuracy can be affected by a number of factors, including the quality of the original data used to create the map, the projection used, and the scale of the map.  High-accuracy maps are important for a variety of applications, including navigation, surveying, and scientific research.

Map Datum

A map datum is a reference point or system used to establish the accuracy and consistency of a map’s coordinate system.  Map datums are typically based on measurements of the Earth’s shape and gravity field, and can vary depending on the geographic region and purpose of the map.  A map’s datum is important for ensuring that it is accurate and can be used in conjunction with other maps and spatial data.

Map Distance

Map distance refers to the actual distance between two points on a map, as opposed to the distance represented on the map itself.  Map distance can be calculated using a variety of methods, including measuring the distance between points using a ruler or calculating the distance using latitude and longitude coordinates.  Accurate map distance is important for a variety of applications, including navigation, surveying, and scientific research.

Map Projection

A map projection is a way of representing the three-dimensional surface of the Earth on a two-dimensional map.  There are many different types of map projections, each with its own strengths and weaknesses.  Some projections, for example, preserve the shape of landmasses but distort their size, while others preserve area but distort shapes.  Choosing the right projection for a particular application is important for ensuring accurate representation of geographical features.

Map Scale

Map scale is the ratio of the distance on a map to the actual distance on the ground.  For example, a scale of 1 50,000 means that one unit of distance on the map represents 50,000 units of distance on the ground.  Map scale is important for understanding the size and distance of features on a map, and can vary depending on the purpose of the map.  For example, a map of a city might have a larger scale than a map of an entire country.

Map Series

A map series is a collection of maps that cover a particular area at different levels of detail or scales.  Map series can be useful for a variety of applications, from navigation to scientific research.  They can be organized into different categories, such as topographic maps, geological maps, or thematic maps, depending on the type of information they convey. Map series can be printed or digital, and are often used in conjunction with other spatial data and tools.


Mapping is the process of creating a map or representation of a geographical area.  It involves collecting and analyzing spatial data, such as topography, land use, and natural resources, and using this information to create a visual representation of the area.  Mapping can be done using a variety of methods, including surveying, satellite imagery, and remote sensing.  Mapping is an important tool for a wide range of applications, from land management to urban planning to environmental monitoring.

Marginal Sea

A marginal sea is a body of water that is partially enclosed by land and connected to a larger ocean or sea.  Marginal seas can be found around the world, and are typically characterized by unique ecological and physical features.  Examples of marginal seas include the Mediterranean Sea, the Gulf of Mexico, and the Sea of Japan.

Marine Terrace

A marine terrace is a flat, elevated landform that is found along the coastline.  Marine terraces are created by a combination of tectonic uplift and erosion, and are typically formed by the action of waves and sea level changes over thousands of years.  Marine terraces can provide important clues to the geological history of an area, and are also important habitats for a wide range of plant and animal species.


A marsh is a type of wetland that is characterized by the presence of non-woody plants and shallow water.  Marshes can be found in a variety of locations, including along coastlines, near lakes and rivers, and in floodplains.  They are important habitats for a wide range of plant and animal species, and also provide important ecological functions such as water filtration, flood control, and carbon storage.  Marshes are also important cultural and recreational resources, and are popular destinations for birdwatching, hiking, and other outdoor activities.

Mass Movement

Mass movement refers to the downslope movement of soil, rock, and other debris under the influence of gravity.  Mass movement can occur on slopes of all sizes and shapes, and can be triggered by a variety of factors, including heavy rainfall, earthquakes, and human activity.  Examples of mass movement include landslides, rockfalls, and debris flows.  Mass movement can have serious environmental and societal impacts, such as property damage, loss of life, and damage to infrastructure.

Mass Wasting

Mass wasting is a general term used to describe the downslope movement of material under the influence of gravity.  It includes a range of processes, from slow, gradual movement of soil and rock to rapid, catastrophic landslides.  Mass wasting is an important geomorphic process that can shape landscapes and influence natural systems, such as erosion, sediment transport, and nutrient cycling.

Maturation Stage

The maturation stage is a stage in the development of a river or stream, characterized by a relatively stable channel and meandering flow pattern. During this stage, the river or stream has reached its maximum level of efficiency in transporting sediment and water. T he maturation stage is typically preceded by the youthful stage, characterized by steep gradients and fast-moving water, and followed by the old age stage, characterized by a wider channel and slower flow.

Maximum Height

Maximum height refers to the highest point or elevation of a particular feature, such as a mountain, building, or wave. M aximum height is an important parameter for a wide range of applications, from construction to oceanography to aviation.  For example, the maximum height of waves can impact shipping and offshore structures, while the maximum height of buildings can impact their structural design and safety.

Mean Sea Level

Mean sea level is the average height of the ocean’s surface, used as a reference point for measuring elevations and depths.  Mean sea level is determined by measuring the height of the ocean’s surface over a period of time, typically 19 years, and taking the average.  Mean sea level is an important parameter for a wide range of applications, from navigation to climate research to land use planning.


A meander is a curve or bend in a river or stream. Meanders are created by a combination of erosional and depositional processes, as the river or stream flows around obstacles and deposits sediment on the inside of the bend.  Meanders can range in size from small curves to large loops, and can influence the shape and behavior of the river or stream over time.


Measure refers to the process of determining the size, quantity, or value of something. In the context of topography, measure can refer to a wide range of activities, from surveying to mapmaking to data analysis.  Accurate measurement is essential for many applications, such as construction, engineering, and environmental monitoring.

Mechanical Weathering

Mechanical weathering is the process of breaking down rock and other materials through physical means, such as freezing and thawing, abrasion, and root growth. Mechanical weathering can occur in a variety of environments and climates, and can be an important factor in shaping landscapes over time.  Mechanical weathering can also play a role in other processes, such as erosion and sediment transport.

Medial Moraine

A medial moraine is a ridge of moraine material that runs down the center of a glacier.  Medial moraines are formed when two glaciers merge, bringing their lateral moraines together to form a single ridge down the center of the combined glacier.  Medial moraines can be important indicators of glacier behavior and can provide insights into past glacial activity.


A meniscus is a curved surface that forms at the interface between two fluids, or between a fluid and a solid surface.  In the context of topography, meniscus can refer to the curved surface that forms at the interface between a liquid and a graduated cylinder or other container used for measuring volume.  Meniscus can affect the accuracy of volume measurements, and must be taken into account when making precise measurements.

Mercator Grid

A Mercator grid is a system of latitude and longitude lines that are superimposed on a Mercator projection map.  The Mercator projection is a cylindrical map projection that preserves straight lines and angles, but distorts areas and distances near the poles.  The Mercator grid allows users to navigate the Mercator projection map using standard latitude and longitude coordinates.

Mercator Projection

The Mercator projection is a cylindrical map projection that was developed by Flemish cartographer Gerardus Mercator in the 16th century.  The Mercator projection is known for its ability to preserve straight lines and angles, making it useful for navigation and maritime purposes.  However, the Mercator projection also distorts areas and distances near the poles, making it less useful for other applications.  Despite its limitations, the Mercator projection remains one of the most widely used map projections in the world.


A meridian is an imaginary line that runs from the North Pole to the South Pole, passing through any given point on the Earth’s surface.  Meridians are used in geographic coordinate systems to measure longitude.  The prime meridian, which passes through the Royal Observatory in Greenwich, England, is used as the reference line for measuring longitude in most parts of the world.


A mesa is a flat-topped mountain or hill with steep sides. Mesas are found in areas of flat terrain, and are typically formed from sedimentary rock that is resistant to erosion.  They can be found in many different parts of the world, but are particularly common in the southwestern United States.

Metamorphic Rock

Metamorphic rock is rock that has been altered by heat, pressure, or other geological processes.  Metamorphism can cause changes in the texture, mineralogy, and chemical composition of the rock, resulting in a new type of rock with different properties than the original.  Metamorphic rocks can be found all over the world and are important in understanding the geologic history of an area.


Meteorology is the study of the Earth’s atmosphere and its phenomena, including weather and climate.  Meteorologists use a variety of tools and techniques to study the atmosphere, including satellite imagery, weather balloons, and computer models.  The field of meteorology is important in understanding and predicting weather patterns, as well as in developing strategies to mitigate the impacts of extreme weather events.


Microrelief refers to small-scale variations in elevation on the Earth’s surface.  This can include features such as bumps, hollows, and small ridges, as well as variations in soil texture and vegetation cover. Microrelief can have important ecological and hydrological implications, affecting soil moisture, nutrient availability, and habitat suitability for various species.  Understanding microrelief is important in many fields, including agriculture, ecology, and urban planning.


Mineralogy is the study of minerals, which are naturally occurring solid substances with a defined chemical composition and crystal structure. Mineralogy is an important field in geology, as it helps scientists understand the formation and properties of rocks and minerals, and provides insights into the Earth’s history and evolution.


A minute is a unit of time equal to 60 seconds.  It is also used as a measure of angle, with one minute of arc equal to one-sixtieth of a degree. In surveying and navigation, minutes are used to measure distance and direction, with one nautical mile equal to one minute of latitude.


A mire is a wetland area that is characterized by peat deposits and a waterlogged, acidic soil.  Mires are often home to a variety of plant and animal species adapted to wetland environments, and can be important habitats for conservation purposes.

Mixed Topography

Mixed topography refers to a terrain that features a combination of different landforms, such as hills, valleys, plateaus, and canyons.  This type of topography is common in many parts of the world and can create unique and varied landscapes that are often used for recreation or scientific study.


In statistics, the mode is a measure of central tendency that represents the most frequently occurring value in a data set.  It is often used in combination with other measures such as the mean and median to describe the overall pattern of a distribution.


A model is a simplified representation of a real-world system that is used to better understand and predict how the system works.  Models are used in a wide range of fields, including physics, engineering, biology, and economics, and can be created using mathematical equations, computer simulations, or physical prototypes.

Model Map

A model map is a simplified representation of a geographic area that is used to study and analyze various aspects of the landscape, such as elevation, land use, and natural resources.  Model maps are often used in urban planning, environmental management, and other fields to help decision-makers understand complex data and make informed decisions.  They can be created using a variety of techniques, including geographic information systems (GIS), satellite imagery, and aerial photography.

Mohorovicic Discontinuity

The Mohorovicic discontinuity, also known as the Moho, is a boundary between the Earth’s crust and mantle that marks a significant change in the composition and density of the underlying rock.  It was first discovered by the Croatian seismologist Andrija Mohorovicic in 1909 and is now recognized as an important feature of the Earth’s interior.


A monocline is a type of geological fold that consists of a single bend or flexure in the rock layers.  It is commonly found in areas of tectonic activity and can create distinctive topographical features such as cliffs, valleys, and plateaus.


A moraine is a type of landform that is created by the accumulation of rock, soil, and debris that is carried by a glacier or ice sheet.  Moraines can take many different forms, including ridges, mounds, and hills, and are often used by geologists to study past glacial activity and the effects of climate change.


Morphology refers to the study of the shape, structure, and form of natural features such as mountains, valleys, rivers, and coastlines.  It is an important field of study in geology, geography, and other earth sciences, as it provides insights into the processes that shape the physical landscape over time. Morphology is also used in other fields, such as biology and linguistics, to describe the shape and structure of organisms and languages, respectively.


A mountain is a large landform that rises above its surroundings and is higher than a hill. Mountains are formed by tectonic forces or volcanism.  They often have steep slopes, sharp ridges, and rugged terrain.  Mountains can be found on every continent, and they are important for their ecological and cultural value. Some of the world’s most famous mountain ranges include the Himalayas, the Andes, and the Rocky Mountains.

Mountain Range

A mountain range is a series of mountains that are connected by high ground. Mountain ranges can be found on every continent and are formed by tectonic forces or volcanism. They often have steep slopes, sharp ridges, and rugged terrain.  Mountain ranges are important for their ecological and cultural value.  They can also affect weather patterns and provide important resources like water, timber, and minerals.  Some of the world’s most famous mountain ranges include the Himalayas, the Andes, and the Rocky Mountains.


A mudflat is a coastal wetland that is covered by mud or silt at high tide and exposed at low tide.  Mudflats are important habitats for a variety of plants and animals, including birds, fish, and invertebrates.  They are also important for their role in nutrient cycling and sediment transport. Mudflats can be found in estuaries, bays, and tidal flats.


A mudflow is a type of mass wasting that involves the rapid downhill movement of a mixture of soil, rock, and water. Mudflows are often triggered by heavy rainfall or melting snow, and they can be very destructive.  They can travel long distances and can cause damage to homes, roads, and other structures. Mudflows can also be dangerous to people and animals, as they can bury or trap them.  Proper land use planning and management can help to reduce the risk of mudflows in areas prone to this type of natural disaster.

Multicolor Map

Multicolor map is a type of map that uses a variety of colors to represent different types of features on the map.  For example, green may be used to represent vegetation, blue for water bodies, and brown for land features.  This type of map provides a clear and visually appealing representation of the landscape.

Multiple Mapping

Multiple mapping refers to the use of more than one map to represent a particular area or feature.  For example, one map may show the topography of an area, while another map shows the vegetation cover.  By combining these different maps, it is possible to create a more comprehensive picture of the area.


Muskeg is a type of wetland that is characterized by deep layers of peat and other organic material.  These wetlands are often found in cold, northern regions where the soil is permanently frozen, and drainage is poor. Muskeg is an important habitat for a variety of plants and animals, including mosses, lichens, and migratory birds.  In terms of mapping, muskeg can be difficult to represent accurately.  Because of the high water content of the soil, the land surface may appear to shift or sink over time, which can make it challenging to create accurate topographical maps.  However, advances in mapping technology have made it possible to create more precise representations of muskeg and other wetland environments.

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