How do you deal with distortion and scale issues when creating maps for different purposes and audiences?

1 Map projection

The first step to deal with distortion and scale is to choose a suitable map projection. A map projection is a mathematical method of transforming the three-dimensional surface of the earth onto a two-dimensional plane. However, no projection can preserve all the properties of the original surface, such as shape, area, distance, direction, and angle. Therefore, different projections have different trade-offs and distortions, depending on the aspect that they try to preserve or emphasize. For example, a Mercator projection preserves angles and directions, but distorts areas and distances, especially near the poles. A Robinson projection tries to balance the distortion of different aspects, but does not preserve any of them exactly. A Lambert conformal conic projection preserves shapes and angles, but distorts areas and distances, especially along the meridians.

2 Map scale

The second step to deal with distortion and scale is to determine the appropriate map scale. The map scale is the ratio between the distance on the map and the corresponding distance on the ground. For example, a 1:100,000 scale means that one unit on the map represents 100,000 units on the ground. The map scale affects the level of detail and generalization that can be shown on the map. A large-scale map shows a small area with more detail, while a small-scale map shows a large area with less detail. For example, a 1:10,000 map of a city can show individual buildings and streets, while a 1:10,000,000 map of a continent can only show major features and boundaries.

3 Map purpose and audience

The third step to deal with distortion and scale is to consider the purpose and audience of the map. The purpose and audience of the map influence the choice of projection, scale, symbols, colors, labels, and layout of the map. For example, a map for navigation needs to show accurate directions and distances, so a conformal projection and a large scale are preferable. A map for education needs to show the relative sizes and shapes of countries and continents, so an equal-area projection and a small scale are preferable. A map for tourism needs to show attractive and relevant features, so a thematic projection and a medium scale are preferable. The map maker also needs to consider the level of knowledge and interest of the audience, and use appropriate language and design to convey the message of the map.

4 Map distortion analysis

The fourth step to deal with distortion and scale is to perform a map distortion analysis. A map distortion analysis is a technique to measure and visualize the amount and type of distortion that occurs on a map due to the projection and scale. There are different methods and tools to perform a map distortion analysis, such as Tissot's indicatrix, graticules, scale bars, and distortion grids. These methods and tools can help the map maker to evaluate the suitability and accuracy of the projection and scale for the intended purpose and audience of the map. They can also help the map user to understand the limitations and biases of the map.

5 Map distortion correction

The fifth step to deal with distortion and scale is to apply a map distortion correction. A map distortion correction is a technique to modify or adjust the map to reduce or compensate for the distortion that occurs due to the projection and scale. There are different methods and tools to apply a map distortion correction, such as cartograms, adaptive scaling, rubber sheeting, and resampling. These methods and tools can help the map maker to improve the representation and communication of the spatial information on the map. They can also help the map user to compare and analyze the data on the map.

6 Map distortion communication

The sixth step to deal with distortion and scale is to communicate the map distortion to the map user. Communicating the map distortion is important to inform and educate the map user about the choices and consequences of the projection and scale on the map. It is also important to acknowledge and disclose the sources of error and uncertainty on the map. There are different ways to communicate the map distortion to the map user, such as metadata, legends, annotations, disclaimers, and references. These ways can help the map maker to provide context and transparency for the map. They can also help the map user to interpret and evaluate the map critically and responsibly.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?