New XY layer from Lat Long (DD) not plotting correctly

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06-19-2013 07:26 AM
AlanMcCarthy
New Contributor II
Hi,

I'm trying to create a new point layer from some Lat and Long coordinates that I have in a table (exp. 44.809662,-73.087322
). I used "Make New XY Event Layer" to plot the points. I have some town parcel layers and the point locations are all from within the parcels so the new point layer should be overlapping the parcels. However, they aren't even close!! I thought it might have been my Lat Long Coordinates so I took Lat Long coordinates from five random locations in the area using Google Maps, imported them into ArcMap as an Excel file and tried again. They all showed up really far away also! Their spatial spread looks correct but they aren't close to the parcel layers.

The projection system and the coordinate systems are the same so I'm not sure what's wrong. Any ideas?

Thanks,
Alan
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14 Replies
MelitaKennedy
Esri Notable Contributor
Hi Alan,

I can think of two possibilities. Are you equating X = longitude and Y = latitude?

When using the Add XY tool, you need to assign the data's current coordinate system. The tool will default to the data frame's coordinate system. Because your points are in lat/lon, you need to assign the appropriate geographic coordinate system.

Melita
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AlanMcCarthy
New Contributor II
Hey Melita,

Yeah the Lat and Long are being equated with the correct locations. I'm also assigning the spatial reference to be the same as the parcel layers I have displayed. After the layer is made sure the Projected Coordinate System, Projection, Geographic Coordinate System and Datum are the same between the points layer and the parcel layers. The data frame coordinate system I've changed to be the same as all the other layers as well.

-Alan
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MelitaKennedy
Esri Notable Contributor
Hi Alan,

Umm, but what coordinate systems are your parcel layers using? Usually they're using a projected one. The XY data is lat/lon. You have to assign the appropriate geographic coordinate system, then ArcMap will project it on-the-fly to match the data frame's coordinate system. At that point, you can export the layer to a feature class and use either the source/native coordinate system or the data frame's.

Melita
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AlanMcCarthy
New Contributor II
Hi Melita,

I'm afraid that I might not be as familiar with some things about projections as I should, but I think I understand. So I apologize if I have some redundant responses.

When I open up the Layer Properties, in the Source Tab for the parcel layer it says "Projected Coordinate System: NAD_1983_StatePlane_Vermont_FIPS_4400". All my other layers also say this in their Source Tabs. Including the point layer I made using "Make XY Event Layer". When using that tool, I set the spatial reference(the option at the bottom) to the Projected Coordinate System: NAD_1983_StatePlane_Vermont_FIPS_4400.

The Geographic Coordinate System I didn't specify when creating the point layer but it was automatically set to Geographic Coordinate System: GCS_North_American_1983, which is the same as all the other layers.

I've noticed that the Data Frames Projected Coordinate System is WGS_1984_Web_Mercator_Auxiliary_Sphere and it's Geographic Coordinate System is Geographic Coordinate System: GCS_WGS_1984.

-Alan
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AlanMcCarthy
New Contributor II
Melita,

I just changed the Data Frame Projection Coordinate System and Geographic Coordinate System to the NAD_1983_StatePlane_Vermont_FIPS_4400 and GCS_North_American_1983 but that didn't change where my plotted points were. They are still appearing really far away from the parcels.

-Alan
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AlanMcCarthy
New Contributor II
Hi Melita,

Soooo, I'm not positive on what happened but I think I fixed it. In arc catalog or by the Define Projection tool I changed the Geographic Coordinate System for the point layer to World WGS_1984. This made the points show up on my parcel layer! In the sources tab though I don't see a projected coordinates system anymore. Maybe it's using the one specified in the Data Frame then?

Lastly, since I was messing with the Data Frame projections should I expect things to be really messed up now. Everything looks good but when I add new layers sometimes a pop up saying that the layer has a different coordinate system than the data frame appears. Should I just always change the layers coordinate system to match the data frame or let it be?

-Alan
MelitaKennedy
Esri Notable Contributor
Hi Alan,

ArcMap has the ability to convert (project!) in-memory between different coordinate systems. To do so, it needs to know both the source and target coordinate systems. The layers or data are the sources. The target is the data frame's coordinate system. You need to leave the layer coordinate system definitions alone. They identify the current reference frame that the data is georeferenced to. If you want to create a copy of the data referenced to a different coordinate system, use the Project Tool.

The warning you're getting is specifically about having different geographic coordinate systems (also know as datums). Even if the data frame or a layer is georeferenced to a projected coordinate system, the projected coordinate system is based upon a geographic coordinate system.

One way to look at it--a geographic coordinate system identify the size and shape of the model of the Earth and where the latitude and longitude lines area. A projected coordinate system converts from this 3D system into a flat plane.

The same location on the ground will have different latitude-longitude values depending on which geographic coordinate system is used. The warning is that there are different geographic coordinate systems in use, and you may need to set some geographic (datum) transformations to reconcile them. The reason that we don't automatically apply geographic transformations is that there are often multiple ones per pair of geographic coordsys or a more accurate transformation may be to use two transformations that convert through a 3rd GCS! Starting at 10.1, we now present a sorted list of transformations in the data frame properties, coordinate system tab, transformation dialog.

Melita
OliviaDeSimone
Occasional Contributor
Hi,

I am sorry to revive this question after its already been resolved, but I am having this same issue.  I understand that having the geographic coordinate systems and projected coordinate systems match between shapefiles does not necessarily mean that they will align properly.  However, I am not sure how to fix the problem so that they do align correctly.

I have lat and long coordinates in an excel file, and I am using Create Feature Class from XY Table in ArcCatalog to create the points.  The other shapefiles I am working with use GCS_NorthAmerican_1983 and are projected into NAD_1983_StatePlane_Pennsylvania_South_FIPS_3702_Feet.  What steps should I take to having my lat and long points properly align?

Thank you!
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OliviaDeSimone
Occasional Contributor
Hi,

I am sorry to revive this question after its already been resolved, but I am having this same issue.  I understand that having the geographic coordinate systems and projected coordinate systems match between shapefiles does not necessarily mean that they will align properly.  However, I am not sure how to fix the problem so that they do align correctly.

I have lat and long coordinates in an excel file, and I am using Create Feature Class from XY Table in ArcCatalog to create the points.  The other shapefiles I am working with use GCS_NorthAmerican_1983 and are projected into NAD_1983_StatePlane_Pennsylvania_South_FIPS_3702_Feet.  What steps should I take to having my lat and long points properly align?

Thank you!
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