The relationship between a globe and a map projection is one of fundamental transformation. A globe is a three-dimensional, scaled model of the Earth that accurately represents its curved surface and geographic relationships. A map projection is a systematic process designed to transfer coordinates from this 3D spherical surface onto a flat, two-dimensional plane. The globe acts as the original source material that must be converted to create a usable, flat map. This conversion is necessary for convenience, but flattening a sphere always introduces stretching or compression.
The Globe: Earth’s True Representation
The globe is considered the only true representation of the Earth because it mirrors the planet’s approximately spherical shape. Earth is technically an oblate spheroid, bulging slightly at the equator due to rotation, and the globe captures this curvature. This faithful representation means the scale is uniform across the entire model, and the areas, shapes, and distances between geographic features are preserved without distortion.
On a globe, angular relationships, such as the intersection of lines of latitude and longitude (the graticule), are shown in their correct spatial configuration. The shortest distance between any two points, known as the great circle route, can be visualized and measured accurately. The globe sets the standard of geographical accuracy against which all flat maps are measured.
The Process of Map Projection
Map projection is the mathematical procedure that bridges the gap between the globe’s curved surface and a flat map. This transformation is not a simple physical flattening, but a calculation that converts spherical coordinates (latitude and longitude) into planar coordinates (x and y). Every projection relies on a unique set of mathematical formulas to achieve this conversion.
Cartographers conceptualize this process using a developable surface—a shape that can be flattened without stretching, such as a cylinder, cone, or flat plane. Cylindrical projections, like the Mercator, imagine wrapping a cylinder around the globe. Conic projections use a cone placed over a section of the sphere, and planar (azimuthal) projections use a flat surface tangent to a single point, typically a pole. The choice and placement of this conceptual surface dictates the mathematical rules used for the coordinate transformation.
The Inevitable Distortion of Flat Maps
Because a sphere is not a developable surface, transferring information from the globe to a flat map results in distortion. This is a fundamental geometric problem, as it is impossible to perfectly preserve all properties of a curved surface when translating it to a plane. The four primary properties subject to this distortion are area, shape (angle), distance, and direction.
Distortion always increases the farther a location is from the point or line of tangency between the conceptual projection surface and the globe. A map projection can be designed to preserve one or two of these properties, but never all four simultaneously. For example, a map that preserves area (an equal-area projection) must sacrifice the correct shape and angular relationships. Conversely, a conformal projection maintains the correct local shapes and angles, but severely distorts the relative sizes of landmasses, especially near the poles.
Selecting Projections Based on Purpose
The inevitability of distortion means mapmakers must choose a projection based on the map’s specific goal. The intended use dictates which geographic property can be distorted and which must be preserved. This explains why hundreds of different map projections have been developed.
For instance, nautical navigation requires a map that preserves correct angular relationships for plotting a compass bearing, making a conformal projection like the Mercator the traditional choice. Maps intended for thematic purposes, such as showing global population density or comparing the size of continents, must use an equal-area projection like the Gall-Peters to ensure accurate visual comparison. World maps meant for general reference often employ a compromise projection, such as the Winkel Tripel, which attempts to balance the distortion of shape and area.