PROJ has a wide and varied user base. Some are highly skilled geodesists with a deep knowledge of map projections and reference systems, some are GIS software developers and others are GIS users. All users, regardless of the profession or skill level, has the ability to contribute to PROJ. Here’s a few suggestion on how:

  • Help PROJ-users that is less experienced than yourself.

  • Write a bug report

  • Request a new feature

  • Write documentation for your favorite map projection

  • Fix a bug

  • Implement a new feature

In the following sections you can find some guidelines on how to contribute. As PROJ is managed on GitHub most contributions require that you have a GitHub account. Familiarity with issues and the GitHub Flow is an advantage.

Help a fellow PROJ user

The main forum for support for PROJ is the mailing list. You can subscribe to the mailing list here and read the archive here.

If you have questions about the usage of PROJ the mailing list is also the place to go. Please do not use the GitHub issue tracker as a support forum. Your question is much more likely to be answered on the mailing list, as many more people follow that than the issue tracker.

Adding bug reports

Bug reports are handled in the issue tracker on PROJ’s home on GitHub. Writing a good bug report is not easy. But fixing a poorly documented bug is not easy either, so please put in the effort it takes to create a thorough bug report.

A good bug report includes at least:

  • A title that quickly explains the problem

  • A description of the problem and how it can be reproduced

  • Version of PROJ being used

  • Version numbers of any other relevant software being used, e.g. operating system

  • A description of what already has been done to solve the problem

The more information that is given up front, the more likely it is that a developer will find interest in solving the problem. You will probably get follow-up questions after submitting a bug report. Please answer them in a timely manner if you have an interest in getting the issue solved.

Finally, please only submit bug reports that are actually related to PROJ. If the issue materializes in software that uses PROJ it is likely a problem with that particular software. Make sure that it actually is a PROJ problem before you submit an issue. If you can reproduce the problem only by using tools from PROJ it is definitely a problem with PROJ.

Feature requests

Got an idea for a new feature in PROJ? Submit a thorough description of the new feature in the issue tracker. Please include any technical documents that can help the developer make the new feature a reality. An example of this could be a publicly available academic paper that describes a new projection. Also, including a numerical test case will make it much easier to verify that an implementation of your requested feature actually works as you expect.

Note that not all feature requests are accepted.

Write documentation

PROJ is in dire need of better documentation. Any contributiions of documentation are greatly appreaciated. The PROJ documentation is available on The website is generated with Sphinx. Contributions to the documentation should be made as Pull Requests on GitHub.

If you intend to document one of PROJ’s supported projections please use the Mercator projection as a template.

Code contributions

Code contributions can be either bug fixes or new features. The process is the same for both, so they will be discussed together in this section.

Making Changes

  • Create a topic branch from where you want to base your work.

  • You usually should base your topic branch off of the master branch.

  • To quickly create a topic branch: git checkout -b my-topic-branch

  • Make commits of logical units.

  • Check for unnecessary whitespace with git diff --check before committing.

  • Make sure your commit messages are in the proper format.

  • Make sure you have added the necessary tests for your changes.

  • Make sure that all tests pass

Submitting Changes

  • Push your changes to a topic branch in your fork of the repository.

  • Submit a pull request to the PROJ repository in the OSGeo organization.

  • If your pull request fixes/references an issue, include that issue number in the pull request. For example:

Wiz the bang

Fixes #123.
  • PROJ developers will look at your patch and take an appropriate action.

Coding conventions

Programming language

PROJ is developed strictly in ANSI C 89.

Coding style

We don’t enforce any particular coding style, but please try to keep it as simple as possible. If improving existing code, please try to conform with the style of the locally surrounding code.


Throughout the PROJ code base you will see differing whitespace use. The general rule is to keep whitespace in whatever form it is in the file you are currently editing. If the file has a mix of tabs and space please convert the tabs to space in a separate commit before making any other changes. This makes it a lot easier to see the changes in diffs when evaulating the changed code. New files should use spaces as whitespace.

File names

Files in which projections are implemented are prefixed with an upper-case PJ_ and most other files are prefixed with lower-case pj_. Some file deviate from this pattern, most of them dates back to the very early releases of PROJ. New contributions should follow the pj-prefix pattern. Unless there are obvious reasons not to.


Commiters are the front line gatekeepers to keep the code base clear of improperly contributed code. It is important to the PROJ users, developers and the OSGeo foundation to avoid contributing any code to the project without it being clearly licensed under the project license.

Generally speaking the key issues are that those providing code to be included in the repository understand that the code will be released under the MIT/X license, and that the person providing the code has the right to contribute the code. For the commiter themselves understanding about the license is hopefully clear. For other contributors, the commiter should verify the understanding unless the commiter is very comfortable that the contributor understands the license (for instance frequent contributors).

If the contribution was developed on behalf of an employer (on work time, as part of a work project, etc) then it is important that an appropriate representative of the employer understand that the code will be contributed under the MIT/X license. The arrangement should be cleared with an authorized supervisor/manager, etc.

The code should be developed by the contributor, or the code should be from a source which can be rightfully contributed such as from the public domain, or from an open source project under a compatible license.

All unusual situations need to be discussed and/or documented.

Commiters should adhere to the following guidelines, and may be personally legally liable for improperly contributing code to the source repository:

  • Make sure the contributor (and possibly employer) is aware of the contribution terms.

  • Code coming from a source other than the contributor (such as adapted from another project) should be clearly marked as to the original source, copyright holders, license terms and so forth. This information can be in the file headers, but should also be added to the project licensing file if not exactly matching normal project licensing (COPYING).

  • Existing copyright headers and license text should never be stripped from a file. If a copyright holder wishes to give up copyright they must do so in writing to the foundation before copyright messages are removed. If license terms are changed it has to be by agreement (written in email is ok) of the copyright holders.

  • Code with licenses requiring credit, or disclosure to users should be added to COPYING.

  • When substantial contributions are added to a file (such as substantial patches) the author/contributor should be added to the list of copyright holders for the file.

  • If there is uncertainty about whether a change is proper to contribute to the code base, please seek more information from the project steering committee, or the foundation legal counsel.


The code contribution section of this CONTRIBUTING file is inspired by PDAL’s and the legalese section is modified from GDAL contributer guidelines