topic Shape file doesn't line up with world imagery in Coordinate Reference Systems Questions

Shape file doesn't line up with world imagery

caitlinpohle — Wed, 03 Sep 2014 13:55:30 GMT

I have a question maybe someone can help with- I have a world imagery layer from Arcgis online and a shape file, they don't quite line up (they are in different coordinate systems). When I change the shapefile coordinate system to match the world imagery layer, it ends up out in space or doesn't show up at all. The layers do not appear in the georeferencing tool bar. Any ideas? I think it must be a simple fix.......

Re: Shape file doesn't line up with world imagery

JorgeOrellana — Wed, 03 Sep 2014 14:12:01 GMT

Could you clarify what you mean by they don't quite line up? Maybe provide a screen shot for us to see.

Do you mean the differences are small and are they consistantly off by the same amount in one direction? or are they off by a random amount in any given direction? There could be many factors at play here including the accuracy of the world imagery or the accuracy of your shp file, even a transformation issue. Without seeing what you are working with it would be tough to pin point it.

Re: Shape file doesn't line up with world imagery

caitlinpohle — Wed, 03 Sep 2014 14:22:05 GMT

Re: Shape file doesn't line up with world imagery

JorgeOrellana — Wed, 03 Sep 2014 14:24:46 GMT

Thanks for posting the screen shot. What coordinate system is your shp file in?

Re: Shape file doesn't line up with world imagery

caitlinpohle — Wed, 03 Sep 2014 14:30:49 GMT

Shape file:

Projected Coordinate System:	Lisboa_Hayford_Gauss_IGeoE
Projection:	Transverse_Mercator

World Img. Layer:

Coordinate System:	WGS_1984_Web_Mercator_Auxiliary_Sphere
Projection:	Mercator_Auxiliary_Sphere

When I change the shape file to WGS_1984 then it gets lost in the ocean near Africa.....

Re: Shape file doesn't line up with world imagery

JorgeOrellana — Wed, 03 Sep 2014 14:48:22 GMT

Caitlin, not sure what you mean by change the shp fiel to WGS_1984 but if you are just changing this and not reprojecting the file through one of the ArcGIS toolboxes and the incorrect paramaters are used, this will give you undesired results. If you are unsure about projections and transformations, you can read more about them in the help files within ArcGIS.

Now to help you a little bit more, a lot of times you will need to apply a transformation to your data when working in different coordinate systems. If you go to View>Data Frame properties you will see the window on he left. If you click on the Transformations button, you will then see the window on the right. I am not sure what area of the world you are working on, but in the drop down menu were it says Using: you have some options, try those out and see if that helps your data align better. if that fails, I would have to say it's just data accuracy issues that unfortunately exists when dealing with different sources of data

Re: Shape file doesn't line up with world imagery

IanMurray — Wed, 03 Sep 2014 15:13:10 GMT

If you need to change the projection of a shapefile, you need to use the Project tool(this will make a new shapefile). If you simply assign it a new coordinate system in properties, you are telling the program this is the projection this data is in(which its not), not projecting it from one coordinate system and datum to another, hence why it ends up in the middle of the ocean.

Re: Shape file doesn't line up with world imagery

caitlinpohle — Wed, 03 Sep 2014 15:15:17 GMT

i'm still fairly new with ArcGIS so it's possible I am making a really simple mistake. So do I want to transform the current coordinate system which is WGS_1984 into Datum_Lisboa_Hayford (which is the coordinate system of the shape file)? When I make these selections and click apply the current coordinate system stays the same, click ok, still the same and when I reopen it it still says the current coordinate system is WGS_1984. Nothing changes.....

Re: Shape file doesn't line up with world imagery

JorgeOrellana — Wed, 03 Sep 2014 15:41:16 GMT

Ok let's take a step back then. A transformation and a reprojection are two different things.

A transformation in a nutshell you are choosing a mathematical calculation used to convert coordinates referenced to from one datum to coordinates referenced to another datum (see here for an explanation About geographic transformations and how to choose the right one | ArcGIS Blog)

In your case you have two one is the Lisboa and the other is WGS84. In order for things to align, you need to tell ArcGIS which mathematical formula to use to convert the respective coordinates (transformations work both ways i.e it goes from WGS to Lisboa and from Lisboa to WGS) which is what I have mentioned in the post above. Changing this setting will always have our data in their original coordinate systems.

Now if you are looking to have both your shp file and the imagery in WGS84 you need to Reproject your data so that they are both in the same coordinate system. This is done through the Projection toolbox which is pretty self explanitory interms of the parameters to enter. However, you will stil need to find out which transformation applies to your area. Once this step is done both your shp file and the imagery will now have the same coordinate system and if done correctly things should line up.

Re: Shape file doesn't line up with world imagery

caitlinpohle — Mon, 08 Sep 2014 11:41:36 GMT

Ok, so after projecting it still looks exactly like the original image I posted above only now the coordinate systems match. I still need help figuring out how to get the two layers to line up....

Re: Shape file doesn't line up with world imagery

JorgeOrellana — Mon, 08 Sep 2014 13:04:43 GMT

Have you tried different transformations? do they yield anything different?

Re: Shape file doesn't line up with world imagery

caitlinpohle — Mon, 08 Sep 2014 13:37:20 GMT

Yes, none of them accurate....

Re: Shape file doesn't line up with world imagery

caitlinpohle — Mon, 08 Sep 2014 16:37:01 GMT

I am sure they are in the same projection now but they still don't line up....

Re: Shape file doesn't line up with world imagery

JorgeOrellana — Mon, 08 Sep 2014 16:44:43 GMT

I am all out of ideas in terms of getting things to line up better. The last conclusion I can make is that either the world imagery is not very accurate in your area of interest or your shp file is innacurate. Sometimes data is captured from a really detailed data set or very course on too and when superimposed on top of other data, discrepencies can occur. Without know much more about how the data was created/obtained I don't know if there's much more I can help with.

Last thing I can think of is acquiring additional data for the area and see how they all line up with one another, which can narrow down which data set is not accurate.

Jorge

Re: Shape file doesn't line up with world imagery

caitlinpohle — Mon, 08 Sep 2014 16:54:46 GMT

I am working in Lisbon, the basemap with world imagery is from arcgis online for 2014 and the other layer is from the university. Isn't there anyway to georeference the layers to make them line up?

Re: Shape file doesn't line up with world imagery

eugeniosanchez — Tue, 09 Sep 2014 08:21:56 GMT

As a test you can try to reproject the raster data (instead the shapefile) to make it the same projection than it (you can do a clip on the raster to cover only your interest zone).

I had a similar problem with spanish raster and GPS data, and reprojecting the GPS data any way I could´t see the data coincidence; and reprojecting the raster (with the cost of the reprojection of raster each time it was repainted) they lined up perfectly.

Re: Shape file doesn't line up with world imagery

JorgeOrellana — Tue, 09 Sep 2014 19:39:22 GMT

You would first need to decide which data is the most accurate, is it the imagery, or is it the shp file?

The issue is with the imagery being a map service and stored online you don't really have a way to georeference the image (unless you export your map as jpg/tif/etc) but you can end up losing the level of detail you need.

You could do a spatial adjust for the shp file (ArcGIS Desktop ) to see if that helps.

With either method you need points that are common to both data sets and if you don't have that, it will be impossible to georeference the two.