topic Re: Layer has no spatial reference in Data Management Questions

Layer has no spatial reference

JuliaGoldsworth — Sun, 09 Apr 2017 04:20:25 GMT

I imported a PDF of an old map and made a layer of polygons for land use. This new layer, though, has no spatial reference. I cannot project the layer because there is no coordinate system to project it from.

How do I give this layer of polygons a spatial reference?

Thank you!

Julie

Re: Layer has no spatial reference

ModyBuchbinder — Sun, 09 Apr 2017 05:03:40 GMT

In ArcMap you can find Define Projection GP tool that will do it.

You need to know what is the correct spatial reference - no tool can find this for you.

Have fun

Re: Layer has no spatial reference

DanPatterson_Retired — Sun, 09 Apr 2017 07:00:24 GMT

Importing an old pdf of a map will just give you a map referenced in pixel coordinate space. You have to ... georeference ... the file in order to provide it with real world coordinates. Just defining its coordinate system will make a bad situation worse.

Re: Layer has no spatial reference

JuliaGoldsworth — Sun, 09 Apr 2017 17:46:02 GMT

The pdf of the old map was georeferenced and it sits nicely in place above the basemap.

That should not affect my new polygons layer. I did Define Projection to the same projection as the other layers in my map, but that has not helped.

Re: Layer has no spatial reference

DanPatterson_Retired — Sun, 09 Apr 2017 18:09:07 GMT

you set the projection of the new polygons to that of the old map then, not your other files. If the new polygons are given a wrong coordinate system, they won't align with your old data. If you want the new file to be in a different coordinate system, you need to define the projection correctly first, then you use the Project tool to produce a new file with the desired coordinate system.

I wrote a visual guide as to what can happen if you mix and match the order of things... define projection vs project