Mapping Locations Using XY Coordinates

Transcription

1 Mapping Locations Using XY Coordinates ArcGIS Desktop 10 Instructional Guide Kim Ricker GIS/Data Center Head (713) Jean Niswonger GIS Support Specialist (713)

2 This guide was created by the staff of the GIS/Data Center at Rice University and is to be used for individual educational purposes only. The exercises outlined in this guide require access to particular software and datasets which are available at Fondren Library. 2

3 Obtaining the Tutorial Data Before beginning the tutorial, you will copy all of the required tutorial data onto your Desktop. Follow the applicable set of instructions below depending on the particular computer you are using. Accessing tutorial data from Fondren Library using the gistrain profile If you are completing this tutorial from a public computer in Fondren Library and are logged on using the gistrain profile, follow the instructions below: 1. On the Desktop, double-click the Computer icon gisdata (\\fon-gis04) (O:) Short_Courses Bringing_Data_Into_ArcGIS_Series Mapping_Locations_Using_XY_Coordinates. 2. To create a personal copy of the tutorial data, drag the XYTutorialData folder onto the Desktop. 3. Close all windows. Accessing tutorial data online using a personal computer If you are completing this tutorial from a personal computer, you will need to download the tutorial data online by following the instructions below: 1. Using a web browser, go to the Introduction to Coordinate Systems and Projections short course webpage at: 2. At the bottom of the webpage, under the Resources section, click the Mapping Locations Using XY Coordinates Tutorial Data link to download the tutorial data. 3. Unzip the XYTutorialData folder. 4. Copy the unzipped XYTutorialData folder to your Desktop or another location of your choice. Ensure that you note the file path of the location you have selected. Any time throughout the tutorial that you see reference to the file path C:\Users\gistrain\Desktop\XYTutorialData, you will need to substitute it with the file path you have just selected. The following step-by-step instructions and screenshots are based on the Windows 7 operating system with the Windows Classic desktop theme and ArcGIS for Desktop 10.1 software with an Advanced license. If your personal system configuration varies, you may experience minor differences from the instructions and screenshots. 3

4 Mapping XY Data Exploring the data First, you will explore the XY data for this exercise that is contained in an Excel file. 1. On the Desktop, double-click the XYTutorialData folder. 2. Double-click Coordinates_ClimateProtectionAgreementMayors to open the file with Excel. This Excel worksheet provides a list of cities whose mayors signed the U.S. Conference of Mayors Climate Protection Agreement as of September 12, This list was obtained from the Climate Protection Center website at Notice that the worksheet also contains the latitude and longitude of the cities in decimal degrees. 3. Close Excel. 4. Close the XYTutorialData folder. Setting up a map document You are now ready to map the XY data in ArcMap. You will begin by opening ArcMap and creating a new map document. 1. On the Desktop, double-click the ArcMap 10.1 icon. 2. In the ArcMap Getting Started window, ensure that My Templates and the Blank Map template are selected. At the bottom of the window, notice the default geodatabase for this map is currently set to C:\Users\gistrain\Documents\ArcGIS\Default.gdb. The default geodatabase should be set to the geodatabase that will contain most of the data for the particular map document you are working on. In this case, you will want to use the geodatabase in your XYTutorialData folder. 3. Next to the Default geodatabase for this map: box, click the Browse button. 4. In the Default Geodatabase window, click the Connect To Folder button. 5. In the Connect To Folder window, select the XYTutorialData folder located on the Desktop. 4

5 Ensure that the XYTutorialData folder is highlighted in blue and not the XYData.gdb geodatabase that appears inside it. You never want to connect directly to a geodatabase, as doing so will prevent you from being able to access any of the data contained inside of it. 6. For Folder:, verify that either the XYTutorialData folder or the C:\Users\gistrain\Desktop\XYTutorialData filepath is listed and click OK. 7. In the Default Geodatabase window, select the XYData.gdb geodatabase and click Add. 8. Ensure the Default geodatabase for this map: box says C:\Users\gistrain\Desktop\XYTutorialData \XYData.gdb and click OK. At this point, it is a good idea to save your map document and to continue saving regularly. 9. On the Standard toolbar, click the Save button. 10. In the Save As window, use the Save in: drop-down box to select the XYTutorialData folder. You will save the map document here, directly inside the XYTutorialData folder, but NOT within the XYData geodatabase. 11. For File name:, type ClimateProtectionAgreementCities and click Save. Remember that, in order for your GIS project to open properly on other computers, you must tell the map document to store relative pathnames to its data sources and take your entire project folder containing all of your data and your map document with you. 12. Click the File menu and select Map Document Properties. 13. Towards the bottom of the Map Document Properties window, click the checkbox to Store relative pathnames to data sources and click OK. 14. On the Standard toolbar, click Save again to store this setting in your map document. Adding a basemap Before you add in your XY data, you will need a basemap so that you will be able to tell if the points are being mapped in the correct locations. It is possible to create your own custom basemap using a variety of data sources, but here you will use a basemap from ArcGIS Online. 1. On the Standard toolbar, click the drop-down arrow to the right of the Add Data button and select Add Basemap. 5

6 2. In the Add Basemap window, select the Streets basemap and click Add. The basemap may take some time to load. 3. If you are asked to enable Hardware Acceleration, click Yes. Displaying XY data Now that you have a basemap, you are ready to map your XY data of cities. 1. On the right side of the ArcMap window, click the Catalog tab. 2. On the Catalog toolbar, click the Go To Default Geodatabase button, which will take you to the default geodatabase you specified earlier. 3. Double-click the Coordinates_ClimateProtectionAgreementMayors Excel file to expand it and view the individual worksheets. 4. Drag Sheet1$ into the Map Display where the basemap is currently showing. Notice at the top of the Table of Contents, the highlighted icon has switched from the first List By Drawing Order button to the second List by Source button. That switch is because the tabular data you just added does not have a graphic component, so it cannot yet be drawn and will not appear in the drawing order view. 5. In the Table of Contents, right-click the Sheet1$ table and select Display XY Data. 6. For X Field:, select the Longitude field. 7. For Y Field:, select the Latitude field. Notice in the Coordinate System of Input Coordinates box, it defaults to the particular projection being displayed in our active data frame, which is currently WGS 84 Web Mercator Auxiliary Sphere. This is the particular projection of the basemap data that we added in, which is the same projection used by most web mapping sites, including Google and Bing. Look in the bottom right corner of the Map Display. You will see coordinates, such as Meters. In order to use this default projection, the XY coordinates in your spreadsheet would have to be similar large numbers in meters, but since they are provided in geographic coordinates of latitudes between -90 and 90 and longitudes between -180 and 180, you will need to specify a geographic coordinate system, rather than a projected coordinate system. 8. In the Coordinate System of Input Coordinates box, click Edit. 9. In the Spatial Reference Properties window, scroll to the top of the list of projections. 6

7 Because the coordinates are in the form of latitude and longitude in decimal degrees, you know you will need to select a geographic coordinate system, rather than a projected coordinate system. While the data could theoretically be in any geographic coordinate system, you will select the World Geodetic System of 1984, commonly abbreviated WGS 84, because this is the reference coordinate system used by the Global Positioning System (GPS). Under most circumstances, this will be the best coordinate system to select when mapping latitude and longitude coordinates. 10. Double-click Geographic Coordinate Systems > World. 11. Select WGS 1984 and click OK. 12. Ensure that your window matches that below and click OK. A warning message appears to let you know that the functionality of your data will be limited until you export the data to a new layer. 13. Click OK. The points should now appear on top of the United States. 14. In the Table of Contents, right-click the Sheet1$ Events layer and select Zoom to Layer. Exporting XY data Since the points appear to be in reasonable locations (rather than in another country or the middle of the ocean), you will want to export them to a new feature class in your XYData geodatabase. Exporting to a feature class will allow you to reuse this points layer in other future map documents without having to go through the display XY data process each time. 1. Right-click the Sheet1$Events layer and select Data > Export Data. Notice that the output feature class defaults to your default geodatabase (C:\Users\gistrain\Desktop\XYTutorialData\XYData.gdb). 7

8 2. For Output feature class:, scroll to the end and rename the feature class from Export_Output to ClimateProtectionAgreementCities and click OK. 3. Click Yes to add the exported data to your map as a layer. Since you are now using a permanent feature class, you may remove your temporary Events layer and the corresponding Excel table. 4. Right-click the Sheet1$ Events layer and select Remove. 5. Right-click the Sheet1$ table and select Remove. If you d like to get a better view of your points, use the navigation tools on the Tools toolbar to zoom in to the continental United States. You have successfully mapped point locations using XY coordinates! Bonus Exercise: Spatial Join The following section is optional and does not contain additional information on mapping locations using XY coordinates. At this point, all of the cities appear on the map, but there are many urban areas that are so densely covered with overlapping points that it becomes difficult to tell exactly how many points there are and to see the underlying data, such as city and state names. In addition, while you can see the spatial distribution of the points, you are not provided with any sort of useful summary of the data. Performing a spatial join will allow you to discover how many participating cities are located in each state, or even county. 1. On the right side of the ArcMap window, click the Catalog tab. 2. Double-click the XYData geodatabase to expand its contents. Notice that the ClimateProtectionAgreementCities feature class you just exported is now contained in this geodatabase. 3. Drag the US_States feature class into the Map Display. 4. When you receive a warning about differences in the Geographic Coordinate Systems, click Close. You will now examine the US_States layer s attribute table. 5. In the Table of Contents, right-click the US_States layer and select Open Attribute Table. 8

9 6. Scroll to the right and browse through all of the attributes. The goal of performing a spatial join is to add a numeric field to the end of this attribute table that tells you how many participating cities are contained within each state. 7. Close the attribute table. 8. In the Table of Contents, right-click the US_States layer and select Joins and Relates > Join. 9. For What do you want to join to this layer?, select Join data from another layer based on a spatial location. 10. For 1., ensure that the ClimateProtectionAgreementCities layer is selected. For 2., notice that by default, each polygon will be given a count field showing how many points fall inside it, so you do not need to pick an additional statistic. If, for example, your cities layer contained an attribute listing the population of each participating city, then, when performing the spatial join, you could check the Sum statistic to calculate the total population residing in participating cities in each state and then calculate what percentage of the state s total population reside in these participating cities. In this case, you do not have such population data available, so you will stick with the default Count attribute. 11. For 3., scroll to the end and rename the feature class from Join_Output to US_States_WithCityCounts and click OK. The new layer should appear at the top of your Table of Contents. 12. At the top of the Table of Contents, click the List by Drawing Order button. 13. Right-click the US_States_WithCityCounts layer and select Open Attribute Table. 14. Scroll to the right and notice the newly added Count_ field. This field tells you how many participating cities are contained within each state. 15. Close the attribute table. Since the new layer contains all of the same information as the old US_States layer, plus the new Count field, you no longer need the US_States layer. 16. In the Table of Contents, right-click the US_States layer and select Remove. 17. Double-click the US_States_WithCityCounts layer to open the Layer Properties window and edit the symbology. 18. Click the Symbology tab. 9

10 19. In the Show: box on the left, click Quantities and leave the default selection of Graduated colors. 20. In the Fields box, use the Value: drop-down menu to select the Count_ field. 21. Click OK. You can now easily tell which states have the largest number of participating cities, though this display does not take into consideration things such as city density and population density or the percentage of the total state population participating. 22. On the Standard toolbar, click Save. 23. Close ArcMap. 10

11 Optional Exercise: Converting Addresses to XY Coordinates If all of your data already comes with a list of the latitudes and longitudes of the points you d like to map, then you are ready to go straight into ArcMap, but what if you have a list of cities or addresses that you d like to map, but you don t know their corresponding coordinates? This section will show you one automated method of generating such coordinates based on address locations. On the actual Climate Protection Center website, only the city is listed for each participating mayor. First, you will explore the data for this exercise that is contained in an Excel file. 1. On the Desktop, double-click the XYTutorialData folder. 2. Double-click Cities_ClimateProtectionAgreementMayors to open the file with Excel. Notice this file is identical to the worksheet you used earlier to map the participating city locations, except that it is missing the latitude and longitude information. In such an instance where you would like to map these cities, you would first have to obtain their coordinates, so you will use an online geocoder. There are many online geocoders, but the one you will be using in this course is called GPSVisualizer. For your future reference, a list of geocoders is maintained by the University of Southern California GIS Research Laboratory at 3. Minimize or Restore Down Excel. 4. On the Desktop, double-click the Mozilla Firefox icon. 5. In the location bar, type gpsvisualizer.com. 6. At the top of the GPSVisualizer window, click Geocode an address. Here, you will see several options for geocoding addresses. Option 2 allows you to geocode multiple addresses and should be used for standard street addresses, but Option 3 allows you to geocode simple locations and is recommended if you are mapping data such as ZIP codes, cities, or states. Since your data table only contains city names, you will use option Under 3. Geocode simple tabular data, click the link to the text/gpx conversion utility. 8. Return to the Excel spreadsheet. 11

12 9. Click the Select All button in the top left corner of the spreadsheet. 10. In the Home tab, click Copy. 11. Return to GPSVisualizer. 12. In the Or paste your data here: box, delete all existing text. 13. Right-click in the Or paste your data here: box and select Paste to copy in the city data from your Excel worksheet. 14. Click Convert. Once the website is finished geocoding your cities, the latitudes and longitudes will be displayed. 15. Towards the top of the window, right-click the link that says following link and select Save Link As. (Yours will have a different download number than shown below.) 16. Double-click the XYTutorialData folder. 17. Rename your file LatLongMayors and click Save. 18. Return to Excel. 12

13 19. At the bottom of the worksheet click the Insert Worksheet button. 20. Click the Data tab. 21. Under the Get External Data section, click From Text. 22. Navigate to select your saved LatLongMayors text file (Desktop > XYTutorialData > LatLongMayors) and click Import. 23. In the Text ImportWizard window, ensure that Delimited is selected and click Next >. A delimiter is simply a character, such as a tab, space, or comma that tells Excel when to move the text into the next column. 24. In the Delimiters box, ensure that Tab is checked and that the column break lines appear in the correct locations in the Data preview box, as shown below, and click Next >. 25. Click Finish. 26. In the Import Data window, click OK. You could now delete any unnecessary columns and save this Excel worksheet to map the XY coordinates just like you did in the first exercise. 13

14 Optional Exercise: Converting DMS to Decimal Degrees Occasionally, you will come across latitude and longitude coordinates listed in Degrees, Minutes, Seconds (DMS) format (27 52'35.1" N, 93 48'54.1" W). However, ArcGIS requires coordinates to be in decimal degrees (DD) format ( , ). This section will show you how to convert coordinates from DMS to DD using Excel. 1. On the desktop, double-click the XYTutorialData folder. 2. Double-click Flower Garden Banks NMS Buoy Locations to open the file with Excel. This Excel worksheet contains the coordinates of all the buoys located in the Flower Garden Banks National Marine Sanctuary. The coordinates were obtained from This dataset provides a perfect example of when it would be absolutely necessary to map point locations using XY coordinates. In the middle of the ocean, there are no physical landmarks or addresses, so location data must be collected using latitude and longitude. Before you can covert DMS coordinates to DD coordinates, it is necessary to separate out the degrees, minutes, and seconds components into their own columns. In Excel, you can divide single cells into multiple columns using either delimiters or fixed width break lines. You will try both methods. Converting text to columns using delimiters 1. Click cell D2 to select it. 2. In the formula bar, highlight the degree symbol ( ) and press Ctrl+C to copy it. 3. Click column D to highlight the entire column. 4. At the top of the Excel window, click the Data tab. 14

15 5. Under the Data Tools section, click the Text to Columns button. 6. In the Convert Text to Columns Wizard, ensure that Delimited is selected and click Next >. 7. In the Delimiters box, uncheck Tab and check Other:. 8. Click the text box to the right of Other: to locate your cursor there and press Ctrl+V to paste the degree symbol ( ). 9. Click Next >. 10. Click Finish. Notice that everywhere the delimiter (in this case, the degree symbol) used to be located, the data has now been split into another column and the delimiter has disappeared. You could repeat this same process twice more, using the apostrophe symbol ( ) and the quotation marks symbol ( ) as the respective delimiters. If your coordinates data had differing numbers of decimal places in each row, repeating this method would be necessary, but, in this case, each set of coordinates has exactly the same number of characters, so using fixed width break lines is possible. Converting text to columns using fixed width break lines 1. Click column E to highlight the entire column. 2. On the Data tab, under the Data Tools section, click the Text to Columns button. 3. In the Convert Text to Columns Wizard, select Fixed width and click Next >. 4. In the Data preview box at the bottom, click on both sides of the apostrophe symbol ( ) to add break lines. 5. Click on both sides of the quotation mark symbol ( ) to add break lines. 15

16 If a break line is in the wrong location, you can click and hold and drag it to a new location. If you need to delete a break line, you can double-click on it. 6. Ensure that the break lines in the Data preview box are placed like those shown below and click Next >. 7. In the Data preview box, click the second column containing the apostrophes to select it. 8. In the Column data format box, select Do not import column (skip). 9. Repeat steps 7 and 8 with the fourth column containing the quotation marks and the fifth column containing the letter W. 10. Click Finish. 16

17 Your spreadsheet should now appear like that shown below. If you have any additional columns, showing because they were not marked to be skipped, delete them now. Using the DMS to DD conversion formula Now that your degrees, minutes, and seconds components are each in their own column, you can use the following formula to convert them into decimal degrees: DD = D+(M/60)+(S/3600). 1. In cell G2, type = to indicate the start of a formula. 2. Type - (negative sign) to indicate these coordinates are west of the prime meridian. 3. Click cell D2 (93 degrees). 4. Type +( (plus sign, open parenthesis). 5. Click cell E2 (35 minutes). 6. Type /60)+( (division sign, 60, close parenthesis, plus sign, open parenthesis). 7. Click cell F2 (49.7 seconds). 8. Type /3600) (division sign, 3600, close parenthesis). 9. Ensure your cell says =-D2+(E2/60)+(F2/3600) and press Enter to finish the formula. 10. Click cell G2 containing the formula you just entered. Hover your cursor over the small black box in the bottom right corner of the highlighted cell as shown below. Notice that your cursor changes from a thick white cross to a thin black cross. 11. Double-click the black box in the bottom right of cell G2 to copy the formula down the table. 17

18 Your longitude coordinates are now in decimal degrees format; however, the cells currently contain formulas, which cannot be read by ArcGIS. To solve this problem, you will copy the values of the equations to a new column. 12. Click column G to select the entire column and press Ctrl + C to copy it. 13. Right-click column H and select Paste Special. 14. Select Values and click OK. Click cell G2 and notice the formula bar contains a formula. Click cell H2 and notice the formula bar contains the actual numeric value of the formula. Since ArcGIS will be using the values you have just pasted in column H, you no longer need columns D through G. 15. Click column D. 16. Hold down Shift and click column G to select columns D through G. 17. Right-click column G and select Delete. 18. Click cell D1 and type Longitude and press Enter. If you wish to test yourself on what you have just learned, insert many columns between column C and column D and practice converting the latitude field from DMS to DD format. Last updated September 26,