Sometimes you're given a set of X,Y or Easting,Northing data in an unknown coordinate format. Here are some tricks to make it easier to determine the correct coordinate format using ExpertGPS.

It's usually a simple task to tell the various lat/lon formats apart, but when given unknown gridded X,Y data, it can be difficult to tell if it is in UTM, US State Plane, or a national grid format, since all three use Eastings and Northings. I help ExpertGPS users convert data every day, and I often get emailed X,Y data without knowing the proper coordinate format. If this ever happens to you, try the following:

Where is this data from?

My first question, when an ExpertGPS doesn't know the exact origin of the data, and therefore the coordinate format used, is "what town does this data cover?" For this tutorial, let's try to figure out the correct format for these coordinates: 145537, 4291885, which should be located somewhere around Alpine, TX.

Since the data is in the United States, and these clearly aren't latitude/longitude coordinates, and US National Grid coordinates would be formatted differently, we know we're dealing with UTM or US State Plane coordinates.

Picking the right US State Plane Coordinate System

ExpertGPS.com has a reference list of every US State Plane coordinate system. Clicking on the link for Texas SPCS lists several possibilities: TX South, TX South Central, TX Central, TX North Central, Texas North, as well as the Texas Statewide Mapping System and Texas Centric Mapping System Lambert.

You could try converting your data using each of these State Plane systems, and see which one gives the correct results. Luckily, ExpertGPS.com also lists the counties each of these coordinate systems cover. A quick Google search for "Alpine TX county" reveals that Alpine is in Brewster County. The Texas SPCS page on ExpertGPS.com shows Brewster County is covered by Texas South Central SPCS (as well as the Statewide and Lambert systems).

Comparing your X,Y coordinates to the formats in ExpertGPS

To make it really easy to find the correct coordinate format, I've built a special feature into the Add Coordinate Formats dialog that instantly shows the coordinates for the location you're viewing on the map in each format listed in the Add Coordinate Formats dialog. To take advantage of this, you'll need to load some data for the general area where your mystery data is located. I used the Go to Address command, and had ExpertGPS create a waypoint at the city center of Alpine, TX. With the map centered on Alpine, I clicked Preferences on the Edit menu, and clicked on the My Coordinate Formats tab. I clicked Add, and the Add Coordinate Format dialog appeared.

As you scroll through the list of coordinate formats listed for Texas, you'll see the results of Alpine's location (lat/lon N30.36061, W103.67280) projected into eastings and northings in each Texas State Plane coordinate format. Scroll through the list until you find a sample that is close to the X,Y data you're importing. In this case, TX South Central (Meters), NAD83 gives these coordinates for Alpine: 151671N, 4288824E, which is very similar to (and only a few kilometers away from) our unknown coordinates: 145537N, 4291885E).

Once you've found the correct coordinate format and datum to use, click OK to add this format to ExpertGPS.

Monica writes:
I was wondering about a state correction for NAD 83 in New Mexico. I am not from here, but have an airphoto that I am working with in this specific system. My GPS unit does not have this grid installed. Would you suggest that I purchase a different GPS unit, or should I have this particular map converted? Are all maps likely going to be in this "State specific" grid system?

You're not going to find a consumer-grade GPS receiver that supports New Mexico state plane coordinates, or any of the other US state plane coordinate systems. Garmin and Magellan simply don't include these professional coordinate systems on their consumer-grade GPS receivers.

The easiest way to convert NM SPCS to something your GPS can use (lat/lon, or UTM) is to use mapping software like ExpertGPS Pro. ExpertGPS will allow you to work with New Mexico state plane coordinates and calibrate your airphoto using state plane coordinates. You can then switch the coordinate format in ExpertGPS to latitude/longitude or UTM, to match your GPS. This makes it very easy to convert between state plane and UTM or latitude/longitude GPS coordinates.

Even when you're viewing a map or aerial orthophoto projected using the New Mexico state plane coordinate system, ExpertGPS Pro will be able to convert your GPS data (waypoints, routes, and tracks) back and forth between NM SPCS NAD83 and whatever format your GPS uses (lat/lon NAD27, UTM WGS84, etc) so that your data always displays in the correct location.

To get started with ExpertGPS, download the 30-day trial and follow these instructions for calibrating and geo-referencing your NM NAD83 airphoto.

Jim D. asks:
Hi, I have and love expertGPS. I've been asked to layout a corner or two for our Placitas Volunteer Library for ground breaking next Sunday. The surveyor of the building sent me, for example, x=1578443.56 y=1567807.68 nad 83, central new mexico, he tells me these are in feet from the principle meridian and baseline. I just want to use my gps, garmin 76 cs to roughly mark a corner or two. Can the expertGPS pro do this, convert to utm's, or lat/long.

ExpertGPS Pro (not ExpertGPS Home) supports all of the US state plane coordinate system formats, and will allow you to enter X,Y data in meters or feet and convert these to lat/lon or send them to your GPS.

To locate the site of your library, I first selected the NM Central NAD83 state plane coordinate system in the My Coordinate Formats tab in ExpertGPS Pro. Do this by clicking Preferences on the Edit menu. Since your surveyor gave you X,Y coordinates that are in US Survey Feet, not Meters, select the second NM Central SPCS entry, the one marked (feet).

Now when you add a new waypoint, you'll be able to enter the coordinates as Eastings and Northings (X,Y) rather than Latitudes and Longitudes. The drop-down list marked Format: lists all of the coordinate format's you've chosen to work with, and so you can now switch back and forth between UTM, lat/lon, and NM Central NAD83 with just a single click. Any time you change the active coordinate format, ExpertGPS Pro will instantly reproject all of your data to the new coordinate format.

To view your newly-marked waypoint in the field, just click Send to GPS. Even though your Garmin GPS can't display NM state plane coordinates directly, you'll still be taken to the right spot. ExpertGPS always communicates with your GPS using WGS84 latitude and longitude, regardless of the display formats and datums you've selected in ExpertGPS or on your GPS receiver.

Related Topics How to Convert Coordinates between Latitude/Longitude and the State Plane Coordinate System Details on all State Plane Coordinate Systems in ExpertGPS Pro

John asks:
I need a tool to convert coordinates in NAD83 decimal degrees to NJ State Plane coordinates.

Converting coordinates using ExpertGPS Pro is an easy, three-step process. Unlike other mapping and GIS programs that force you to work in a single coordinate format, ExpertGPS allows you to switch between coordinate formats at any moment. Click Preferences on the Edit menu, and click the My Coordinate Formats tab.

Select your starting format - in this case, Decimal Degrees (latitude and longitude) in NAD83 datum. While you're in this dialog, go ahead and add the NJ State Plane Coordinate system. To do so, drill down in the Location tree to United States. Once you select New Jersey, the Format list will update to show all of the SPCS formats available in New Jersey. There are two. The default uses meters, and the one marked (feet) uses US Survey Feet. Choose which datum you require: NAD27 or NAD83/WGS84.

You can add as many coordinate formats as you want - just remember, the one that is highlighted is the active coordinate format, and this is the one that ExpertGPS will use when displaying your GPS data, and when importing new data. So make sure NAD83 decimal degrees is selected now.

Add your data - either by hand using the New Waypoint command, by receiving it from your GPS, or by using Import on the File menu. Your data is in NAD83 decimal degrees at this point.

To do the conversion, simply go back to the My Coordinate Formats tab in Preferences, and select New Jersey SPCS NAD83. When you make the change, ExpertGPS will reproject all of your data from lat/lon to NJ State Plane Coordinates.

You can copy and paste your data right into Excel, or use Export on the File menu to export your reprojected data to a shapefile, CAD drawing, or other format.

Related Topics ExpertGPS Help: My Coordinate Formats dialog State Plane Coordinate Formats in ExpertGPS

Casey from Louisiana asks:
Hi. I am trying to determine a coordinate point location using a property description in an oil and gas lease that was drafted using the Louisiana Coordinate System of 1927. Does your Louisiana North FIPS 1701 mapping system contain the same coordinates as the Louisiana Coordinate System of 1927? My property description uses X and Y coordinates. For example, the coordinates X=1696760.5 and Y=580448.3, using the Louisiana North FIPS 1701 state plane coordinates in your software, delivers a topo map in Oklahoma to my screen - those coordinates should direct me to a map in Bossier Parish, LA. Could you please help me determine where I am going wrong? I believe this software could continue to help my company, but I need to figure out if the software is compatible with my property descriptions. Thanks.

Why don't these Louisiana Coordinate System of 1927 locations map properly in ExpertGPS?

ExpertGPS Pro lists two versions of each State Plane Coordinate System: one in Meters, and one in US Survey Feet. You'll need to select the correct one for the coordinates you'll be working with. You'll also need to know the correct datum (NAD27 or NAD83/WGS84).

As a general rule of thumb, NAD83 State Plane coordinates use meters, and NAD27 coordinates use the US survey foot. That's the case for your data, given in the Louisiana Coordinate System of 1927. When I selected the "feet" version of the LA North SPCS in ExpertGPS' Add Coordinate Format dialog, your X,Y coordinates mapped to the correct location in Bossier Parish.

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