Map Projection in GIS

A projection map is a mathematical process that allows us to convert three-dimensional coordinates on the earth's surface—whether the reference shape representing the earth is a sphere or an ellipsoid—to coordinates represented on a plane surface, which is the map two-Dimensional coordinates or Grid Coordinates. In other words, projection is the process that allows us to convert the latitude and longitude values of a location into the eastern and northern coordinates required to label this location on a map (the shape resulting from the projection process is also known as projection).

The process of converting the stereoscopic shape of the Earth into a flat form (a map) cannot be completed in its entirety, and any method of projecting maps will result in "Distortion." Different methods of map projection attempt to maintain one or more of the following characteristics between the actual target on the ground and its image on the map (some characteristics cannot be combined):

·        Match in spaces

·        Match in distances

·        Match in directions

·        Match in corners

·        Match in shapes

Types of map projections

There are projection types that preserve distances and are referred to as Equidistance Projections, projection types that preserve shapes and angles together, but in limited areas, and are referred to as Conformal Projections (which are most commonly used in cadastral applications), and projection types that preserve areas and are referred to as Equal-Area Projection.

There are four types of map projections:

·   Cylindrical Projections: result from the projection of the earth’s surface onto a cylinder, which either touches the earth vertically or cuts it or touches the earth transversely or diagonally.

·    Conical Projection:  arises from the projection of the earth's surface onto a cone, which either touches the earth vertically or cuts it.

·     Azimuthal Projection: They arise from the projection of the Earth's surface onto a plane that either touches the Earth vertically at a specific point or cuts it in a circle.

·      Other private projections.

Commonly the shape of the geographical area to be projected plays a crucial role in determining the most suitable projection method. For instance, if the shape of the area is semi-circular, we select a method for projecting its two features, a cylindrical projection method for semi-rectangular areas, and a conical projection method for semi-triangular areas.

Mercator map projection

A cylindrical projection satisfies the condition that lines of latitude and longitude intersect at perfectly right angles. The scale is true at the equator or at two Standard Parallels of latitude equidistant from the equator. This site is often used in nautical charts.

Transverse Mercator Projection

This projection is the result of the Earth being projected onto a cylinder that touches it at a Central Meridian. This projection is often used for areas whose north-south extension is greater than their east-west extension. The distortion (in scale, distance, and area) increases as we move away from the Central Meridian; therefore, when using this projection, we employ the concept of slices, where the width of one slice - in the direction of the east - is three or four degrees of longitude so that the amount of distortion is not excessive. The edges of the slice whose central longitude is located in the center. The Mercator projection is utilized on maps of numerous nations, including Egypt and the Britain.

Universal Transverse Mercator Projection

It is the most common type of map projection on a global level and its abbreviation is UTM. Because it is one of the projections used in GPS technology devices, its significance has also grown in recent years.

·   The UTM projection is dependent on finding a way to draw maps of the entire world by dividing the earth into 60 zones, each covering 6 degrees of longitude, so that each segment has a UTM projection with a Central Meridian centered on this segment.

·      The UTM projection segments extend from latitude 80 south to latitude 84 north.

·    The tranches are numbered from No. 1 to No. 60, beginning at 180º West longitude, so that the first tranche extends from 180º west to 174º west and has a central longitude of 177º west.

·        Every 8 degrees of latitude divides each longitudinal slice into squares.

·      There shall be a special letter - as a name - for each of these squares, and the letters start from the letter C in the south to the letter X in the north, with the exclusion of the letters I and O (because they are similar to the English numbers!).

·    The factor scale is equal to 0.9996 at the central longitude, so as we move away from the central longitude, the maximum value of the scale factor at the slice's edges is 1.00097 at the equator or 1.00029 at latitude 45º.

Sinusoidal Equal-Area Projection

In this space-preserving projection, the latitude circles are only perpendicular to the central meridian, whereas the rest of the longitude lines are curved in a manner similar to sin curves (hence the name of this projection: the sinusoidal projection). The scale of the drawing is only accurate at the central longitude and latitude, and this projection is used for areas that extend in a north-south direction.

Lambert Conformal Conic Projection 

This projection utilizes the cone (not the cylinder as in previous projections), in which the areas and shapes are identical at the two Parallels Standards, the distortion increases as we move away from them, and the directions are correct in a limited number of areas. In North America, this projection is used.

Lambert Azimuthal Equal-Area Projection

This planar projection (as opposed to a cylinder or cone) is often used to plot vast oceanic regions. With the exception of the central meridian, all other meridians are curved.

Orthographic Projection

Azimuth projection (i.e., the use of the plane in projection) is frequently employed to display a generalized image or perspective of the hemisphere. In it, both areas and shapes are distorted, while the distances on the equator and other latitude circles are accurate.