If I take a set of GIS data (shapes, points, lines, etc) and convert the projection many times, will there be a loss in accuracy in the data?

The reason I ask is that I have a dataset from OSM which is in EPSG:3857 (WebMercator) and I want to convert to WGS84, then to the next projection, and so on. Ideally, I don't want to work on a copy of the original dataset. Instead, I want to update the data in-place.

However, this won't work if each time I re-project the data there is a loss in coordinate accuracy. After several conversions to whatever projection the data may be way off.

Specifically, I am using proj4 and PostGIS

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    – Ian Turton
    Jan 20, 2022 at 11:08
  • 1
    Note accuracy and precision are different things, you can have high accuracy and low precision, and high precision and low accuracy
    – nmtoken
    Jan 20, 2022 at 11:20
  • I think the real question is do you really need to reproject many time ? (you may set your data in a suitable projection for your whole extend and use on the fly reprojection for display purpose). If you tell more about your workflow and end goal somebody may suggest a way that wont degrade your data
    – J.R
    Jan 20, 2022 at 11:41
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    I'd be more worried about the performance cost of re-reprojecting. Attributes can be joined and updated, or better still, stored once and joined as needed. Coordinate precision is managed by the trig fuctions used to get there; starting with the same values will result in the same results, but deprojecting might result in slightly different values. As a rule, it's poor practice to make a habit of projecting back and forth without a compelling reason.
    – Vince
    Jan 20, 2022 at 11:45
  • We have multiple (100s) Azimuthal Equidistant projections. I would be pre-generating a tile set for each projection so performance is not the issue beyond the initial render. Accuracy needs to be good as ideally we should not have too much drift in the values. However it's just for display on a browser based map so it doesn't need to be absolutely accurate to the meter. I'm trying to think of a way how to generate vector tiles in all these reproductions in the fastest way. Given that there is so much data (planet) it's a lot of crunching and will no doubt be very slow.
    – JT-Hello
    Jan 20, 2022 at 12:29

1 Answer 1


Yes, it can do, but whether this is important to you will depend on your use case.

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