A map projection is a system which gives the relationship between the position of points on the earth and on the map. Because the physical earth’s surface is irregular, then it is hard to perform calculations on the results of size (measurement). Was selected for a field that is regularly approaching physical field is the field of the earth ellipsoid with certain quantities. Map is a drawing of the earth’s surface on a flat surface in a smaller size.
In this case the position of the dots on the map are determined to bracket system x and y, being the position of points on the Earth’s surface is determined by latitude and longitude. In the construction of a map projection, the earth is usually described as a sphere (with radius R = 6370.283 km). In this case the ellipsoid volume equal to the volume of the ball. Ball field is what will be taken as the mathematical form of the earth’s surface to simplify the calculation.
A small area (a maximum of 30 km x 30 km) can be considered as a flat area, so that mapping of the area can be directly drawn from the results of measurements in the field, without using a map projection system. The main problem in the presentation of map projections is curved to flat fields. A curved field can not be extended to a flat plane without going to undergo changes (distortions), while a map is said to be ideal if:
1) broad right
2) forms correctly
3) The right direction
4) The right distance
The fourth requirement will not be met, but always had to sacrifice other requirements. That can be done is to reduce the distortion as small as possible to meet one or more requirements ideal map, namely by:
1) Divide the mapped region into parts that are not so wide.
2) Using a flat field or fields that can be leveled (if it is leveled undistorted), the field of cones and cylinders fields
How to depiction of a curved shape to a flat shape can be done by using a specific mathematical formula. Presentation of the surface of the Earth on a flat plane needed to express the position of the points on the earth’s surface into a flat plane coordinate system that can later be used for the calculation of distances and directions. Another goal is for graphical representation that can be used to help study the topography, climate, vegetation, shelter and so on are usually associated with large areas.
Projection method or transformation can be classified as follows:
1) Projections directly, ie from the ellipsoid to the plane of projection.
2) Projected double, a transformation of the ellipsoid to field the ball and then on the field the ball into the field of projection.
UTM system with the system WGS 84 is often used in mapping regions of Indonesia. UTM using a cylinder that encloses the ellipsoid with the position of the cylinder axis perpendicular to the vertical axis ellipsoid (the axis of rotation of the earth) so that the ellipsoid and cylinder tangent is the line of longitude that coincide with the ellipsoid. UTM projection system defined on a horizontal two-dimensional position (x, y) using a cylindrical projection, transversal, and conform the earth cut in two standard meridian. The entire surface of the earth is divided into 60 sections called UTM zone.
Each zone is limited by two meridians at 6 ° and has its own central meridian. For example, zone 1 starting from 180 ° to 174 °, zone 2 at the start of 174 ° to 168 °, continue eastward until the zone 60 which starts from 174 ° E to 180 ° E. Limits of latitude in this coordinate system is 80 ° S to 84 ° N. Each section has a width of 8 degrees that division starting from 80 ° latitude towards the north.
Part degrees from the bottom (LS) denoted starting from the C, D, E, F, up to X (letters I and O are not used). So part degrees to 80 ° S to 72 ° S notated C, 72 ° S to 64 ° S notated D, 64 ° S to 56 ° S notated E, and so on.
Figure 7. UTM Zone World
Each UTM zone has its own coordinate system with zero point at the intersection of the central meridian to the equator. To avoid negative coordinates, central meridian rated initial abscissa (x) 500,000 meters. For a zone located at the south of the equator (LS), also to avoid negative coordinates equatorial coordinates given initial value (y) 10,000,000 meters. As for the zone that is located in the north of the equator, equatorial retains ordinate value of 0 meters.
Indonesian territory is divided into nine zones UTM, starting from the meridian 90 ° E to 144 ° E with a boundary parallel (latitude) 11 ° S and 6 ° N. Thus begins the Indonesian territory of zone 46 (central meridian 93 ° East) to zone 54 (central meridian 141 ° E).