## General principles of map projections

In digital cartography, map projections are used to represent the three-dimensional surface of the earth on a two-dimensional map. A map projection involves the mathematical process of transforming the earth’s spherical or ellipsoidal shape into a flat map.

There are several general principles that are used in map projections, including:

- Preservation of one or more properties of the earth’s surface, such as area, shape, distance, or direction.
- Distortion of other properties of the earth’s surface, as no map projection, can preserve all properties without distortion.
- The use of standard lines of latitude and longitude to define the location of features on the map.
- The selection of a central point or line, known as the standard parallel or central meridian, about which the distortion is minimized.
- The use of mathematical formulas to transform the spherical or ellipsoidal coordinates of the earth into planar coordinates for the map.

Each projection has its own advantages and disadvantages, it’s important to choose the right one depending on the use case and the desired representation of the data in the map.

## Classification of Map Projection

Map projections in digital cartography can be classified into several categories:

**Cylindrical projections:**These projections present the Earth as a cylinder with a flat top and bottom. Examples of cylindrical projections include Mercator and Transverse Mercator.**Conic projections:**These projections present the Earth as a cone with a circular base. Examples of conic projections include Albers Equal Area and Lambert Conformal Conic.**Azimuthal projections:**These projections present the Earth as a flat surface with a central point. Examples of azimuthal projections include Orthographic and Gnomonic.**Pseudocylindrical projections**: These projections present the Earth as a cylinder with a distorted top and bottom. Examples of Pseudocylindrical projections include Mollweide and Hammer-Aitoff.**Perspective projections:**These projections present the Earth as if it is viewed from a specific point in space. Examples of perspective projections include Stereographic and Oblique Mercator.

Each projection has its own advantages and disadvantages, and the choice of projection depends on the specific application and the desired level of accuracy.

## Cylindrical, conical, and zenithal projections

**Cylindrical projections**are map projections that involve projecting the surface of the Earth onto a cylinder. This results in a map that has straight lines of longitude and latitude, but at the cost of distorting areas near the poles. Common examples of cylindrical projections include the Mercator projection and the Transverse Mercator projection.

**Conical projections**involve projecting the surface of the Earth onto a cone. This results in a map that has curved lines of longitude and latitude and is often used for small-scale maps of regions such as North America. Common examples of conical projections include the Albers Equal Area Conic projection and the Lambert Conformal Conic projection.**Zenithal projections**involve projecting the surface of the Earth onto a plane that is perpendicular to the Earth’s surface. This results in a map that has straight lines of longitude and latitude, but at the cost of distorting areas that are not directly facing the projection point (the “zenith”). Common examples of zenithal projections include Stereographic projection and Gnomonic projection.

Digital cartography involves the use of computer software and technology to create and manipulate maps. This can include the use of GIS software, digital map data, and geospatial analysis tools to create and manipulate maps in various projections.

## Coordinate System in Digital Cartography

Map projections are used to represent the Earth’s surface on a flat surface, such as a map or screen. These projections involve mathematically transforming the three-dimensional spherical surface of the Earth onto a two-dimensional plane. In order to accurately locate points on a map projection, a coordinate system must be used.

There are several different coordinate systems that can be used in digital cartography, including:

**Geographic coordinate systems:**These use latitude and longitude to specify the location of a point on the Earth’s surface. The most commonly used geographic coordinate system is WGS 84 (World Geodetic System 1984), which is used by GPS and other navigation systems.**Projected coordinate systems:**These use a specific map projection to transform the Earth’s surface onto a flat surface. The coordinates used in a projected coordinate system will vary depending on the projection used. Common projected coordinate systems include UTM (Universal Transverse Mercator) and State Plane Coordinate Systems.**Grid reference systems:**These use a grid system, such as a UTM grid or a British National Grid, to specify the location of a point on a map. These systems are useful for navigation and for measuring distances on a map.**Custom coordinate systems:**These are specific coordinate systems that have been created for specific projects or regions. They may use a combination of different types of coordinates, such as a projected coordinate system with a grid reference system.

Overall, the choice of coordinate system will depend on the purpose of the map and the level of accuracy required. It is important to ensure that the correct coordinate system is used and that the coordinates are correctly transformed when working with multiple data sources.

## UTM (Universal Transverse Mercator)

UTM (Universal Transverse Mercator) is a map projection system used in digital cartography to project the earth’s surface onto a flat surface. It divides the earth’s surface into 60 zones, each 6 degrees of longitude wide, with a central meridian in the center of each zone. Each zone is projected using a transverse Mercator projection, which preserves the correct shape and area of features within that zone, but distorts features outside of it. UTM is commonly used for large-scale maps, such as those used for navigation and land management, and is also compatible with GPS technology.

## Choice of projections

There are several different types of projections that can be used in digital cartography, each with their own unique characteristics and uses. Some of the most commonly used projections include:

**Mercator Projection**– This projection is commonly used for navigation and is known for its ability to maintain consistent direction and shape across a map.**Robinson Projection**– This projection is known for its ability to maintain accurate area relationships across a map while minimizing distortion.**Gall-Peters Projection**– This projection is known for its ability to provide a more accurate representation of the relative size of countries and land masses.**Winkel Tripel Projection**– This projection is known for its ability to minimize distortion in both shape and area.**Miller Cylindrical Projection**– This projection is known for its ability to provide a more accurate representation of the relative size of landmasses and its cylindrical shape.**Mollweide Projection**– This projection is known for its ability to provide a more accurate representation of the relative size of countries and land masses.

Ultimately, the choice of projection will depend on the specific needs and goals of the cartographer or mapping project.