Map projections convert latitude and longitude coordinates on a spherical Earth into two-dimensional planar coordinates by applying a mathematical transformation. They define a coordinate system and allow measurement of horizontal and vertical distances to establish positions of geographic features. Creating a projection involves selecting an Earth model (sphere or ellipsoid) and transforming geographic to planar coordinates. Common projections preserve either shapes, areas, distances or directions depending on the mapping needs.

1. Map Projection
Map projections are representations of a sphere
(the earth) in two-dimensions. A mathematical
transformation is required in order to convert
Latitude & Longitude. A coordinate system is
usually defined by a map projection, a spheroid, a
datum, one or more standard parallels, a central
meridian. It is a system to measure horizontal &
vertical distance so that a geographic feature’s
true position can be established.

2. Construction of projection
The creation of a map projection involves two
steps:
• Selection of a model for the shape of the Earth
or planetary body (usually choosing between a
sphere or ellipsoid).
• Transformation of geographic coordinates
(longitude and latitude) to Cartesian (x,y)
or polar plane coordinates.

3. Shape of the earth and the models
• A geodetic datum is a reference from which measurements
are made. In surveying and geodesy, a datum is a set of
reference points on the Earth's surface against which position
measurements are made and an associated model of the shape
of the Earth (reference ellipsoid) to define a geographic
coordinate system. Horizontal datums are used for describing
a point on the Earth's surface, in latitude and longitude or
another coordinate system. Vertical datums measure
elevations or depths.
• As the earth is a geoid accurate representation of the mean
sea-level surface becomes more complex.
• Hence, the datum WGS84 is used in GPS to represent the
entire earth for this purpose.

4. Scale Factor
The scale of a map is the ratio of distance on the
map and the corresponding ground surface.
• The scale depends on location, but not on direction.
• Scale is constant along any parallel.
• Combination of the above: the scale depends on
latitude only, not on longitude or direction. This
applies for the Mercator projection in normal aspect.
• Scale is constant along all straight lines radiating
from a particular geographic location. This is the
defining characteristic of an equidistant projection
such as the Azimuthal equidistant projection.

5. Types of Map Projection
The choice of a suitable projection on any occasion
depends on the extent of area concerned and the
purpose of mapping.
• Equal Area, Aitoff’s Lambert’s Cylindrical, Sanson-
Flamsteed’s Projection: areas in Tropical Zone and
Temperate Zone (maintain discred shape & distance at
large)
• Polar Equidistant, Polar Guonomic, Polar Stereographic
Projection: Polar regions
• Two Standard Conic Projection: areas of limited extent
(eg. France)
• Bonne’s Projection : relatively smaller areas

6. Transverse Mercator Projection
The Transverse Mercator map projection is an
adaptation of the standard Mercator projection. When
paired with a suitable geodetic datum, the transverse
Mercator delivers high accuracy in zones less than a
few degrees in east-west extent.

7. Transverse Mercator Projection
The Transverse Mercator map projection is an
adaptation of the standard Mercator projection. When
paired with a suitable geodetic datum, the transverse
Mercator delivers high accuracy in zones less than a
few degrees in east-west extent.