module 9 working with xy data. overview geographic datums working with coordinates in arcmap go to...

Module 9 Working with XY Data

Overview Geographic Datums Working with Coordinates in ArcMap Go To XY Transformations On the Fly Add XY Data

Geographic Datums Coordinates pairs, XY, are based on a particular grid; a defined reference system In order to work with coordinates, you need to know the Source reference system The coordinates E-5 mean very little without knowing what map or page in an atlas the E-5 references A Geographic Datum is a definition for coordinates based on a particular calculation of the Earths size and shape; it is a grid reference system of Latitude and Longitude based on a specific model of the Earth, e.g. the GRS80 spheroid

Working with Datums in ArcMap Common Datums: WGS84 and NAD83 (and the older NAD27) Datums define spherical coordinates: Lat/Long define locations on a specific 3D model of the Earth, or spheroid It is imperative to know which spheroid or Datum your Latitude and Longitude coordinates reference. Otherwise, its similar to having the coordinates E-5 without knowing to which map the coordinates refer

Geographic Coordinate Systems Latitude and Longitude represent a Geographic Coordinate System or unprojected coordinates, i.e. represent locations on the 3D model of the Earth Distances vary between Degrees Longitude Ex. Longitude meridians converge at poles; Distances between 1 Longitude much smaller in higher latitudes than at the equator Because of this, you cannot calculate Acres using a geographic coordinate system; the data must be projected in order to calculate acres

Working with Datums in ArcMap Any number of projections may be applied to these spherical coordinates in order to flatten the Earth to two dimensions The same projection could be calculated using different Datums: UTM projection based on NAD27 UTM projection based on NAD83 UTM projection based on WGS84 Many other projections and Datums!

Geographic Datums Why do we Care? Latitude and Longitude coordinates are only part of the information You need to know what Datum the lat/long coords reference in order to display them correctly in ArcMap Sometimes you may need to convert lat/long coordinates from one Datum to another, a process known as Transformation See ESRI Help, Wikipedia, and other resources for more info In general, consult your GIS Specialist before converting data between Datums

Working with Datums in ArcMap The Web Soil Survey stores and serves data in Geographic Coordinates based on WGS84. These are Degrees, Minutes, Seconds or equivalent Decimal Degree units, not projected Many other datasets may be received in WGS84 You wont typically need to transform reference data to NAD83 for use in ArcMap You should avoid data transformation unless you are sure you know what you are doing You will need to set the transformation method in the ArcMap so that datasets with different Datums will display correctly using ArcMaps project on the fly

Transformations On the Fly When you add data to ArcMap that has a different Datum than the Data Frame projection, you will receive this warning. Click Transformations button

Verify the input Datums From the dropdown, Select:WGS_1984_(ITRF00)_To_NAD_1983 Note: it doesnt matter whether you are going from WGS84 to NAD83 or vice versa the SAME transformation should be used Transformations On the Fly

Click OK Click Close Transformations On the Fly * This transformation method will now be applied to all datasets added to the data frame that have this source Datum

Working with Coordinates in ArcMap Typically work with Decimal Degrees Latitude/Longitude (unprojected) West Longitude values must be negative Must know Datum Convert Spreadsheet Coordinates to desired Datum or Set ArcMap Data Frame projection/transformation appropriately How to find specific locations or create data using Coordinate data

Working with Coordinates in ArcMap Two main methods of working with XY coordinates in ArcMap: 1. Go To XY. tool Finds XY locations in a map Quickly locates one XY point at a time Not good for locating multiple points End product is a graphic 2. Add XY Data Adds a new map layer called an Event based on a table containing XY coordinates Quickly locates numerous XY points at once Not efficient for locating a single point Save Event layer out to shapefile or feature class to make permanent

1. Go To XY Click the XY icon from the main toolbar to open the Go To XY tool Next click the dropdown and select the format of your coordinates

Go To XY Copy/Paste or Type the coordinates Tip: X value is Longitude Tip: Longitude must be negative for Western hemisphere Click the Flash Button to see the location Note Options on the Go To XY toolbar Here Ive clicked Add Point and Add Callout

Go To XY Here Ive added a point and callout for another set of coordinates Note that each point and callout are graphics only You may move the callouts without moving the point using the Select Elements tool Ideal for quickly finding a location or adding quick points and labels to a map

Go To XY To Save the point graphics as shapefile or feature class: Select the points using the Select Elements tool

Go To XY Load the Drawing Toolbar if necessary Drawing dropdown >> Convert Graphics to Features Navigate and Name the Output dataset OK

2. Add XY Data Why use add XY data method? Locate the following: OSDs that have coordinates NASIS pedons that have coordinates Hardcopy field notes and 232s that have coordinates written on the form File >> Add Data >> Add XY Data

1.You must have coordinates 2.Create a table in Microsoft Excel that has at least 2 columns All columns must have headers (no spaces in header names) Add additional columns if necessary Enter coordinates under appropriate X Y headers Step 1 Create a Table Add XY Data XYSeries -102.93544.001Naff -103.15744.504Pilotbutte -104.00144.105Cheney Required Columns Additional Column Coordinates in this example are in Decimal Degrees ColumnHeaders* *NO spaces or special characters!

Add XY Data Notes We recommend using Microsoft Excel since most people are familiar with this program. You can use Microsoft Access, Microsoft Excel, txt, and dbf files when creating your tables. Be aware, some file types limit decimal places which may affect your projections of XY data when working in decimal degrees, which is another reason to use Excel. We recommend using X and Y for your column headers, but you can name the columns whatever you want as long as you dont have spaces and they dont exceed 10 characters. IMPORTANT: You can use either Latitude/Longitude or UTM (Easting/Northing) coordinates in the table. X = Longitude and Easting Y = Latitude and Northing

Add XY Data Notes cont IMPORTANT: Latitude and longitude data must be in the form of decimal degrees for this tool to work and the longitude data must have a negative sign in front of it. UTM coordinates eastings are NOT negative and no sign is needed Data in the form of degrees minutes seconds must be converted to decimal degrees. The conversion formula is below: Example GPS point: 44 degrees, 27 min, 40 sec 96 degrees, 47 min, 28 sec Latitude in DD = (44 + (27/60) + (40/3600)) = 44.46111 Longitude in DD = (-96 + (47/60) + (28/3600)) = -96.79111 Notice the negative sign in front of the longitude data

Add XY Data File >> Add Data >> Add XY Data Browse to table If using Excel file, select the Sheet name Select: X for X field Y for Y field Select Edit to choose coordinate system if necessary Click Ok to run Step 2 Run ADD XY Tool

Add XY Data A new layer will be added to your table of contents and the points will display in ArcMap. The points displayed are in an Event layer and are temporary. They may be saved in the Map Document (.mxd) To make permanent: Right click on the layer (event) Data >> Export Data Export to shapefile or geodatabase

Exercise Become familiar with Go To XY tool Calculate Coordinate values for Existing Points Use Add XY Data tool to create new points

Open Module 9 >> XY_data.mxd Click XY tool Double-click Module 9 >> Lat_Longs.txt to open in Notepad This text file contains the coordinates for two points Set the Units to Decimal Degrees using the dropdown Copy/Paste the coordinates into the Go To XY tool Add Points and labels for each location ( ) Select both Points using the Select Elements tool Add the Drawing Toolbar if necessary Drawing dropdown >> Convert Graphics to Features (use data frame projection) Navigate to the Module 9 directory and save the points as TwoPoints.shp Add them to your map Delete the graphics so that you only have the point shapefile based on these coords >> Save. NOTE: You must add POINTs and not simple Call-out labels in order to convert to points Go To XY

Open the table for the TwoPoints.shp created in the last step. The shapefile includes a Name field that contains the original coordinates used in the XY tool Calculate Point Coordinates What DATUM do these coordinates represent? Are they WGS84, NAD27, NAD83?

ANSWER: We added the coordinates to a data frame with a spatial reference UTM zone 14 NAD83. ArcMap located the coordinates based on this spatial reference; that is, using the XY tool, we essentially said, Show me where these latitude/longitude coordinates are in UTM zone 14 NAD83 and then we converted those graphics to points. The original coordinates were thus displayed as NAD83 coordinates We exported the points out to a shapefile using the Data Frame coordinate system, so the resulting TwoPoints shapefile is projected to UTM zone 14 NAD83 Now well calculate THREE different sets of coordinates for those same two points: Geographic (lat/long) NAD83 UTM zone 14 (NAD83) Geographic (lat/long) WGS84 First, well add the necessary fields to the TwoPoints.shp table: Open the TwoPoints.shp table if necessary Table >> Add Field

Name the field: X_n83 Type: Text Length: 25 characters OK Name the field: Y_n83 Type: Text Length: 25 characters OK Repeat these steps to add another field for the Y value: RESULT:

Name the field: X_utm Type: Text Length: 25 characters OK Name the field: Y_utm Type: Text Length: 25 characters OK Now repeat these steps to add fields to hold the UTM coordinates: RESULT:

Name the field: X_wgs84 Type: Text Length: 25 characters OK Name the field: Y_wgs84 Type: Text Length: 25 characters OK Now complete these steps a third time adding fields for WGS84 coordinates: RESULT:

Right-click on the X_n83 field >> Calculate Geometry >> X Coordinate of Point Use the coord system from data source i.e. the shapefiles projection, not the data frame Select Decimal Degrees for units OK

Result: X values match the original coordinates from the.txt file that was used to generate the points The labels also match the original values but have been rounded to 9 decimal places (the labels have been rounded, but the actual coordinates have not been we just calculated the actual coordinates and they match the original values)

Now Calculate the Y Coordinate Right-click on the Y_n83 field >> Calculate Geometry >> Y Coordinate of Point Use the coord system from data source i.e. the shapefiles projection, not the data frame Select Decimal Degrees for units OK

Result: Y values match the original coordinates from the.txt file that was used to generate the points The labels also match the original values but have been rounded to 9 decimal places (the labels have been rounded, but the actual coordinates have not been we just calculated the actual coordinates and they match the original values)

Now well calculate UTM Coordinates Right-click on the X_utm field >> Calculate Geometry >> X Coordinate of Point Use the coord system from data source i.e. the shapefiles projection, not the data frame Select Meters for units OK

Repeat for Y UTM Coordinates Right-click on the Y_utm field >> Calculate Geometry >> Y Coordinate of Point Use the coord system from data source i.e. the shapefiles projection, not the data frame Select Meters for units OK

We now have both lat/long and UTM coordinates for the two points Next well calculate where these two points are referencing a different Geographic Datum: WGS84

Right-click on Layers >> PropertiesSelect the Coordinate System tab and collapse all the folder to match the graphic

Expand the Geographic folder Expand the World folder Select WGS 1984 Do not click OK yet.

Verify that WGS_1984 is Selected Click the Transformation button Select the WGS_1984 (ITRF00) to NAD_1983 Transformation from the list (probably first option) Click OK

The Data Frame coordinate system is now in Geographic, WGS84 The data layers are un-projected and appear squarer Calculate Point Coordinates

Open TwoPoints table if necessary Right-click on X_wgs84 >> Calculate Geometry Calculate the X coordinate Select the Data Frame coordinate system Select Decimal Degrees

Right-click on Y_wgs84 >> Calculate Geometry Calculate the Y coordinate Select the Data Frame coordinate system Select Decimal Degrees

We now have three sets of coordinates calculated for the same two points: The source coordinate system for the TwoPoints shapefile is UTM 14 NAD83 We calculated the lat/long coordinates based NAD83 (the source coordinate system) We calculated the UTM coordinates based on UTM 14 NAD83 We calculated the lat/long coordinates based on the WGS 1984 Datum by changing the Data Frame coordinate system, setting the appropriate Transformation method, and calculating the points using the Data Frame coordinate system instead of the TwoPoints source coordinate system In the resulting table we can see the differences between NAD83 and WGS84 coordinates This is why when you have coordinates it is imperative to know the original source, i.e. Datum they reference

Exercise Become familiar with Go To XY tool Calculate Coordinate values for Existing Points Use Add XY Data tool to create new points

If you have a large number of coordinates it is impractical to copy/paste them into the Go To XY tool one at a time as demonstrated in the last step Instead, use the Add XY Data tool to Display coordinates in a spreadsheet lat/long coordinates as Decimal Degrees The coordinates are NAD83 coordinates Optionally Export these points to a Geodatabase or shapefile

Set the Data Frame Coordinate System to match the coordinates in the spreadsheet, i.e. NAD83 Open the Data Frame Properties Right-click on Layers >> Properties >> Coordinate System Tab >> Geographic Coordinate Systems folder >> North America >> Select NAD_1983 Click OK The coordinates are NAD83 lat/long The ArcMap data frame was set to WGS84 in the previous step and we need to reset it to NAD83 Otherwise, ArcMap will locate the coordinates as if they were WGS84 coordinates!

Add XY Data Now well add the coordinate values from the spreadsheet as Events File >> Add Data >> Add XY Data

Add XY Data >> Navigate to the Excel spreadsheet called coords.xlsx in the Module 9 directory >> Double-click on the file and select the coords$ Worksheet (You must select a specific Worksheet; often it will be the default name Sheet1 in the list) >> Add

Add XY Data The fields in the spreadsheet are named X and Y ArcMap attempts to auto-populate the X and Y fields but you should always verify this is correct NOTES: Field headers can be named anything but with No Spaces No Special Characters And the coordinate values must be either numeric or General data type Verify and click OK

Add XY Data The Events layer is added to the Table of Contents as coords$.Events Now that weve verified that they show up correctly well save them out to the geodatabase

Add XY Data Right-Click on the Events layer >> Data >> Export Data

Add XY Data Change the Type to File and Personal Geodatabase feature classes Navigate Module 9\NE159.gdb\FDS_NE159\ Name the new feature class myNewPts Save Yes, Add the new layer to the Map

Add XY Data Now a little clean-up: R-click and Remove the Events layer Change the symbol for the ne159_p layer to the big green dot. Turn on the ne159_p layer

Add XY Data The coordinates in the spreadsheet were derived from the ne159_p data layer and should match

Exercise Summary Use the Go To XY tool to locate one or a few points Optionally save the graphic points using the Drawing toolbar >> Convert Graphics to Features Use Calculate Geometry to retrieve XY coordinates for Point datasets Optionally change the data frame projection to retrieve different coordinate values, i.e. projected versus geographic Use Add XY Data to display a spreadsheet of coordinates called Events in ArcMap Once you verify that they appear in the correct location, optionally save as a permanent data layer Remember to select the ITRF00 transformation when displaying data in WGS84 and NAD83 at the same time. Do not convert data between datums without consulting your GIS Specialist.

Bonus Question: What if you have a spreadsheet of WGS84 coordinates and you want to display them with your NAD83 data?

module 9 working with xy data. overview geographic datums working with coordinates in arcmap go to...

Documents

datums slide

geographic coordinates

latlong coordinates

coordinates e

different datums

spherical coordinates

xy data slide

reference data