常见问题：加拿大有哪些常见的投影和地理坐标系？

Note: 
This article is contributed by Esri Canada. 

The projections and geographic coordinate systems (GCSs) used to define data in ArcGIS are an important part of working with GIS data. Below is an overview of some of the most common projections and geographic coordinate systems for Canada.

Geographic coordinate system: A reference system that uses latitude and longitude to define the locations of points on the surface of a sphere or spheroid. A geographic coordinate system definition includes a datum, prime meridian, and angular unit.

Commonly used geographic coordinate systems in Canada

• North American Datum of 1927 (NAD 1927)
• NAD 1927 CGQ77
• NAD 1927 definition 1976 for Ontario
• North American Datum of 1983 (NAD 1983)
• NAD 1983 CSRS98 (Canadian Spatial Reference System)
• Average Terrestrial System of 1977 (ATS77)

Projected coordinate system: A projected coordinate system is defined by a geographic coordinate system, a map projection, parameters required by the map projection, and a linear unit of measure. Every map projection distorts distance, area, shape, direction, or some combination thereof.

Commonly used projected coordinate systems in Canada

• Universal Transverse Mercator (UTM)
• Modified Transverse Mercator (MTM)
• 10-degree Transverse Mercator (10TM)
• 3-degree Transverse Mercator (3TM)
• Albers Equal Area Conic
• Lambert Conformal Conic (LCC)
• Stereographic

For more information about the terms geoid, ellipsoid, spheroid, and datum, refer to What do the terms geoid, ellipsoid, spheroid and datum mean, and how are they related?