topic Re: jpgs and world files in ArcGIS Pro Questions

jpgs and world files

KeithAddison1 — Tue, 10 Jun 2025 14:41:02 GMT

When I throw a jpg with a jgw (or jpgw) world file into Pro, they locate correctly when thrown into a map, but the program can never recognize the coordinate system, it always says no coordiate system defined. I'm trying to understand more fully what goes on when this happens. I can to use the define projection tool to fix this, it gets irritating though. Is this because the coordinate system name is not baked anywhere into the file header? The sids & tifs I get from 3rd parties all seem to have the coordinate system name baked into the header somewhere because Arc can read and tell you which coordinate system it is in, no define projection step needed. Is this because jpgs can't bake this information into their headers? What makes jpgs different than the tifs and sids in this regard?

Re: jpgs and world files

RobertCao — Tue, 10 Jun 2025 21:08:00 GMT

Hi @KeithAddison1 ,

Have you tried enabling the 'Use world file to define the coordinates of the raster' option to see if that resolves the issue?

Thanks,

Robert

Re: jpgs and world files

KeithAddison1 — Tue, 10 Jun 2025 21:11:38 GMT

Yep, I'll try disabling it just for curiosity.

Re: jpgs and world files

Luke_Pinner — Wed, 11 Jun 2025 03:06:45 GMT

@KeithAddison1 wrote:
...
Is this because the coordinate system name is not baked anywhere into the file header?
...
Is this because jpgs can't bake this information into their headers? What makes jpgs different than the tifs and sids in this regard?

Yes. JPEGs do not have any spatial capability inherently, they're a simple image format. SIDs are a specially designed spatial raster format. TIFFs can have custom tags in the file and the GeoTIFF spec uses this to spatially enable TIFF files. World files don't contain a coordinate system, just the parameters for an affine transformation matrix. ArcGIS can determine JPEG coordinate system from *.prj or *.aux.xml files, but sounds like you don't have these sidecar files.

Re: jpgs and world files

RichardDaniels — Wed, 11 Jun 2025 20:38:25 GMT

example of a .prj file contents for WGS 1984.

GEOGCS["GCS_WGS_1984",
DATUM["D_WGS_1984",
SPHEROID["WGS_1984",6378137.0,298.257223563]],
PRIMEM["Greenwich",0.0],
UNIT["Degree",0.0174532925199433],
AUTHORITY["EPSG",4326]]