GEOGRAPHIC
INFORMATION SYSTEM
PROJECTIONS
AND
COORDINATES
Projections and Coordinates
Map Projection
A mathematical
transformation formulated to create
a flat map sheet out of the three-
dimensional surface of the earth
which is considered a sphere or
spheroid.
Projections and Coordinates
Types of Map Projection
Different methods to
reduce the “stretching” of surfaces
when they are flattened.
1. Conic
Projections and Coordinates
Types of Map Projection
Different methods to
reduce the “stretching” of surfaces
when they are flattened.
2. Cylindrical
Projections and Coordinates
Types of Map Projection
Different methods to
reduce the “stretching” of surfaces
when they are flattened.
3. Planar
Projections and Coordinates
Coordinates
The features on a map reference the
actual locations of the objects they represent
in the real world. The positions of objects on
the earth's spherical surface are measured in
geographic coordinates.
While latitude and longitude can locate
exact positions on the surface of the earth,
they are not uniform units of measure; only
along the equator does the distance
represented by one degree of longitude
approximate the distance represented by one
degree of latitude.
To overcome measurement difficulties,
data is often transformed from three-
dimensional geographic coordinates to two-
dimensional projected coordinates.
Projections and Coordinates
Geographic Coordinates
One method for describing the position of a
geographic location on the earth's surface is
using spherical measures of latitude and
longitude. They are measures of the angles (in
degrees) from the center of the earth to a point
on the earth's surface.
Latitude angles are measured in a north-
south direction. The equator is at an angle of 0.
Often, the northern hemisphere has positive
measures of latitude and the southern
hemisphere has negative measures of latitude.
Longitude measures angles in an east-west
direction.
Longitude measures are traditionally based
on the Prime Meridian, which is an imaginary
line running from the North Pole through
Greenwich, England to the South Pole. This
angle is Longitude 0. West of the Prime For example, the location of Davao City is roughly
Meridian is often recorded as negative Latitude "plus 7 degrees, 5 minutes" and Longitude “plus
Longitude and east is recorded as positive. 125 degrees, 33 minutes."
Projections and Coordinates
2D
Projected Coordinates
Projected coordinate systems are any
coordinate system designed for a flat surface,
such as a printed map or a computer screen.
2D and 3D Cartesian coordinate systems
provide the mechanism for describing the
geographic location and shape of features using x
and y values.
3D
The Cartesian coordinate system uses two
axes: one horizontal (x), representing east-west,
and one vertical (y), representing north-south.
The point at which the axes intersect is called the
origin. Locations of geographic objects are
defined relative to the origin, using the notation
(x,y), where x refers to the distance along the
horizontal axis, and y refers to the distance along
the vertical axis. The origin is defined as (0,0).
Philippine Reference System of 1992
The Philippine Reference System of 1992
or PRS92 is a homogeneous national
network of geodetic control points
(GCPs), marked by survey monuments or
mojons, that has been established using
Global Positioning System (GPS)
technology. GPS is an all-weather, high
precision, global satellite positioning
system that revolutionized navigation and
surveying operations.
PRS92 serves as the country's standard
coordinate reference system for all survey
and mapping activities. It provides the
means through which base and thematic
datasets can be consistently inter-related
geographically.
The NHA GIS data buildup
• Identifying Data sets required
• Determine the details / fields that must be
associated with the data
• Determining which type the data should be
(point, line, polygon)
• Determining method of collection (plotting,
GPS, others)
• Determining software required
• Determining repository of data
• Determining frequency of update
• Determining methods of access / publication of
data
