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Plotting XY coordinates - DMS, DD, units problem?

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06-07-2018 01:06 PM
deleted-user-sXb0qqZ4LmSL
New Contributor

I received some tabular data that I believe came from a GPS unit that had XY coordinates in a strange (at least to me) format - sample: 30.23.379, 097.44.220. I assumed these to be in degrees, minutes, seconds so I converted them to decimal degrees to plot in ArcMap. Plotting them (in NAD 1983) gets me in the right city, but they are not in the right location of the study area. See attached snip that shows the points and the study area that the points are supposed to fall within (in purple). The fact that the spread of points is 'larger' than the study area makes me think that there is some type of units issue.

I then converted the decimal degrees to feet and meters and tried to plot in State Plane and UTM, respectively, but no success - the points go to "no man's land". Likewise when I try to use the feet or meters coordinates and plot in NAD83.

Is there an issue with the original data? Or is there something else I can do to manipulate these points in the right location? Calling all you smart people!

FYI we have reached out to the contractor who supplied this data to inquire about the original units and coordinate system since that is unknown at this time.

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12 Replies
MelitaKennedy
Esri Notable Contributor

It's Austin, Texas, so Texas Central zone. 

NAD27 US survey feet, x = 2.5 million, y = 250k

NAD83 meters, x = 900k, y = 3 million

NAD83 US survey ft, x = 3 million, y = 10 million

NAD83 Texas statewide meters, x = 1.2 million, y = 900k

NAD83 UTM 14N meters, x = 600k, y = 3.3 million

There are 2 other statewide systems. It could also be in another state plane zone like south central.

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DanPatterson_Retired
MVP Emeritus

we will have to wait for Angela to provide the extents of the data then.

thanks Melita

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deleted-user-sXb0qqZ4LmSL
New Contributor

Melita, it appears you are correct that the data is in degrees, decimal minutes rather than degrees, minutes seconds. Once I calculated decimal degrees with the correct formula, my points are now falling within my study area. This is exactly the reason that my data was "scaled" improperly. Thank you very much!

In regards to the projection/shifting issue, when I projected the data to StatePlane, I found that the data is actually (incorrectly) in the StatePlane Texas S Central zone, rather than the Central zone. 

Thank you all for your replies!

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