Projections

This web site provides information on over 140 geospatial projection methods. For hundreds of years, cartographers worked on methods for flattening the earth from spherical coordinates (geographic) to projected coordinates (rectangular). The largest collection of these algorithms is in the PROJ library. These algorithms provide a huge variety of ways of flattening the earth with each method providing a different impact on the distortion resulting from the projection.

The content here solves two problems with projection methods. The first is finding an optimized boundary for clipping data before it is projected. Without this, some projections have areas that are greatly distorted and can even overlap with other projected areas. This web site contains examples of optimized boundaries for all projection methods for default settings while others are available online and the complete toolkit for creating the boundaries is available in GitHub. The second problem is visualizing the distortion that is inherent in projected data. The Methods page provides the ability to view distortions for methods with default parameters while the toolkit can provide distortions for any combination of supported settings.

Classes of Methods

This web site presents a new classification of projection methods based on their flexibility in representing the earth. Click on one of the items below to see the methods for each classification.

1. Dynamic Poles: The most flexible methods that allow the origin and the position of the poles to be moved. Moving the poles is accomplished by using the General Oblique Transformation on the selected method.
2. Dynamic Longitude Of Origin: Methods that can display any region of the earth and can have the longitude of origin shifted.
3. Static Global: Methods to display the earth but without changing the position of the projected data.
4. Specific Region: Methods designed specifically for one region of the earth.
5. Projection Transform: These are not traditional projection methods but instead modify another projection methods outputs. These provide a great deal of flexibility in we can use them to move the poles of many of the methods.

Types of Solutions

The solution to finding an optimized bounding box required a variety of approaches based on the nature of the projection method.

• No Solution: The Projection Transforms rely on another projection method so they will not have a solution. The Oblique Cylindrical Equal Area method contains the ability to rotate the coordinates and move the poles and we are still looking for a robust solution for this method.
• Global: These methods do not require a bounds until we limit the desired amount of distortion.
• Bounding Boxes: Some methods required the bounds of geographic coordinates to be inherently limited. Some of these were methods for a Specific Region.
• Valid Polygons: A number of methods have extreme distortion issues and/or have areas that intersect or fold over. These required an approach that created boundaries without these issues.
• Distance Distortion: This set required a valid polygon to be found and required the amount of distortion for distances to be limited to have produce reasonable results.