Reproject Data or On-the-Fly for Web Mercator services?

Question

Original User: Steve Clark

I know there are two options to create WGS services if your data is in a different coordinate system (like State Plane): Reproject the data to WGS or to change the mxd to on-the-fly transformation. Both have their advantages and disadvantages, the former is time-consuming and the latter comes at a performance cost.

I assume there are a lot of sites out there that have their data in State Plane (or other) coordinate system and publish map services as WGS for sharing etc. Which one of the two options is best practice or commonly done.

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SteveClark · Answer

Thank you. "unless you have a very large dataset and/or a very complex map document" begs the question as to what is considered a very large dataset or very complex map document. I suspect we may have both but I do not know the metrics to determine. I guess what I can do know is to run SystemTools and compare our current map service to one that is projecting on the fly.

Anonymous User · Answer

Original User: crafty762I know there are two options to create WGS services if your data is in a different coordinate system (like State Plane): Reproject the data to WGS or to change the mxd to on-the-fly transformation. Both have their advantages and disadvantages, the former is time-consuming and the latter comes at a performance cost.

I assume there are a lot of sites out there that have their data in State Plane (or other) coordinate system and publish map services as WGS for sharing etc. Which one of the two options is best practice or commonly done.

The answer to this question depends on the use case(s) involved and the particular goals you are trying to achieve.  What is best practice for one organization may not be best practice for another organization.  If you are required to maintain your spatial data in a specific coordinate system due to strict accuracy requirements, then you might lean toward not reprojecting all of your data but instead simply change the data frame of your map document before publishing your service.  Yes, doing this does come at a bit of a performance hit but it's generally pretty negligible unless you have a very large dataset and/or a very complex map document.  On the other hand, it you don't have a preference on which coordinate system is used to maintain your data then you could reproject it as a one-time project and go forward from there.  Then you wouldn't take a performance hit when publishing the service.  Does this make sense?