The Earth is a three-dimensional sphere. A map is a two-dimensional flat surface. Getting from one to the other requires a map projection — a mathematical transformation that converts the curved surface of the Earth to a flat plane.
The Distortion Problem
Every projection distorts something. It is mathematically impossible to represent a curved surface on a flat plane without distortion. Different projections preserve different properties: conformal projections preserve shape but distort area; equal-area projections preserve area but distort shape; equidistant projections preserve distance from a specific point.
Common Projections
Web Mercator (EPSG:3857)
Used by Google Maps, OpenStreetMap, and most web mapping applications. Preserves shape locally but severely distorts area at high latitudes. Greenland appears as large as Africa, though it is actually about 14 times smaller.
Lambert Conformal Conic
Widely used for mid-latitude regions like Canada. Preserves shape well across a wide east-west extent. Statistics Canada uses a Lambert projection for national maps.
Universal Transverse Mercator (UTM)
Divides the world into 60 north-south zones, each 6 degrees wide. Provides accurate measurements within each zone. Canada spans UTM zones 7 through 22.
For web maps: Web Mercator. For measuring areas in Canada: Lambert Equal Area or Albers Equal Area. For measuring distances: UTM for the relevant zone. For national thematic maps: Statistics Canada Lambert.
Learn how addresses become coordinates in Geocoding.