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In short, a projection is used to 'flatten' the ellipsoidal shape of the earth to rectangular coordinate system (e.g., a map). A datum is a specific, known point on or in the Earth that is used for reference. A projection uses the datum as a point of reference, it's location on Earth.

In GIS, there are two types of "coordinate systems": Geographic Coordinate System (latitude and longitude) and Projected Coordinate System (X and Y). Both geographic coordinate system's and projected coordinate systems use a datum for reference.

• A geographic coordinate system is not projected (not flat), they are in latitude and longitude. Think of a round globe, not a flat map.

• Projected coordinate systems on the other hand are "flat" - but still need a point of reference (datum) to define locations in space.

In other words, the datum is used to determine the point of origin on Earth by referencing a central point inside a 'model' of Earth.

• A projection is used to 'flatten' the ellipsoidal shape of the earth to rectangular coordinate system (i.e, to make a 'roundish' globe into a flat map).
• A datum is a specific, known location on or in the Earth that is used as a reference.

All GIS coordinate systems use a datum as a point of reference (i.e., it's location on Earth).

There are two types of "coordinate systems": Geographic Coordinate System (latitude and longitude) and Projected Coordinate System (X and Y).

• A geographic coordinate system is not projected (not flat), they are in latitude and longitude. Think of a round globe (i.e., Google Earth), not a flat map.

• Projected coordinate systems on the other hand are "flat" - but still need a point of reference (a datum) to define locations in space.

Both geographic coordinate systems and projected coordinate systems use a datum to reference the coordinate system to a location on Earth.

In short, a projection is used to 'flatten' the earth used for maps. A datum is a point of reference. A projection uses the datum as a point of reference, it's location on Earth.

In GIS, there are two types of "coordinate systems": Geographic Coordinate System (latitude and longitude) and Projected Coordinate System (X and Y). Both geographic coordinate system's and projected coordinate systems use a datum for reference.

• A geographic coordinate system is not projected (not flat), they are in latitude and longitude. Think of a round globe, not a flat map.

• Projected coordinate systems on the other hand are "flat" - but still need a point of reference (datum) to define locations in space.

In other words, the datum is used to determine the point of origin on Earth by referencing a central point inside a 'model' of Earth.

In short, a projection is used to 'flatten' the ellipsoidal shape of the earth to rectangular coordinate system (e.g., a map). A datum is a specific, known point on or in the Earth that is used for reference. A projection uses the datum as a point of reference, it's location on Earth.

In GIS, there are two types of "coordinate systems": Geographic Coordinate System (latitude and longitude) and Projected Coordinate System (X and Y). Both geographic coordinate system's and projected coordinate systems use a datum for reference.

• A geographic coordinate system is not projected (not flat), they are in latitude and longitude. Think of a round globe, not a flat map.

• Projected coordinate systems on the other hand are "flat" - but still need a point of reference (datum) to define locations in space.

In other words, the datum is used to determine the point of origin on Earth by referencing a central point inside a 'model' of Earth.

WGS84 is a "horizontal datum" - a mathematical representation of the Earth used to reference points.

Both geographic coordinate system's and projected coordinate systems can use WGS84 as the datum they reference. The difference is geographic coordinate systems are not projected, they are in latitude and longitude. In other words, not all measures of latitude and longitude are equivalent - they need to be referenced to a datum - most likely WGS84. Projected coordinate systems on the other hand are "flat" - but still need a point of reference (datum) to define locations in space.

In other words, the datum is used to determine the origin of points on Earth by referencing a central point inside the Earth model.

In short, a projection is used to 'flatten' the earth used for maps. A datum is a point of reference. A projection uses the datum as a point of reference, it's location on Earth. 

In GIS, there are two types of "coordinate systems": Geographic Coordinate System (latitude and longitude) and Projected Coordinate System (X and Y). Both geographic coordinate system's and projected coordinate systems use a datum for reference.

• A geographic coordinate system is not projected (not flat), they are in latitude and longitude. Think of a round globe, not a flat map.

• Projected coordinate systems on the other hand are "flat" - but still need a point of reference (datum) to define locations in space.

In other words, the datum is used to determine the point of origin on Earth by referencing a central point inside a 'model' of Earth.