. Look back to the first practical and set up the new map as before, up until the stage where you are selecting a projection in the “Data Frame Properties”. This time, use the following projection file: “PredefinedGeographic Coordinate SystemsWorldWGS 1984”. Set the display units to “Degree Minutes Seconds”. Then add the following layer to the map: “Atlantis.shp”. This is an invented dataset of pretend Atlantean sites in France (the author used Atlantis to ensure that nobody could ever confuse this for real world data). We need a background map layer, which can be downloaded from the following link: If the link does not work, simply complete the exercise using the layer already added to the map. Save the file and extract it to your project directory. Then add the layer “FRA_adm0.shp” to your map. Make sure that it is underneath the find spot layer in the layer list. Save your progress. If you watch the status bar as you move the cursor around the map, you will see that we are currently working in degrees of longitude and latitude. However, to perform any spatial analyses correctly, we need to project our map so that we can work with straight lines rather than curved arcs. and search for “project”. Launch the “Project” tool. In the “Input Dataset…” box select the “Atlantis” layer. Click on the file open icon next to the “Output dataset…” box and select a sensible location. Name your new file “Atlantis_Merc.shp”. Next, click on the icon next to “Output Coordinate System” . Click on “Select” in the form that appears. We are going to use the traditional Mercator projection. Find the following projection file: ““PredefinedProjected Coordinate SystemsWorldMercator (world).prj”. This is a whole world projection, so likely to be less accurate for this relatively small region of the planet than some other projections. However, it illustrates the point of this exercise well. Click on “Add”, then “OK”, to return to the “Project” tool. Next, click on “OK” and the tool will run. Repeat the above procedure for the “FRA_adm0.shp” layer, saving it as “France_Merc.shp”. Remove the two new layers from the map (if they have been added automatically) and save your progress. Open up a new ArcMap window (by launching the program again in the conventional manner). Create a new blank map as before, but this time set the projection in the “Data Frame Properties” to the Mercator projection used above. Set the map units to “Kilometers” (you may need to do this after adding the data). Add the two new shapefiles that you just created to the map “Atlantis_Merc.shp” “France_Merc.shp”. Save your progress. Now, if you switch between the two ArcMap windows, you can see the large difference in the shape of the country (also see the two maps below). Notice how the sites in the Atlantean layer are still in the same position in the projected map relative to the coastline. The shape of the projected map should also appear more familiar, as the Mercator projection provides the view of the world that most of us are used to. However, there are many other (often better) projections out there: for your own study area, ask local archaeologists which are the most commonly used. If you were to gather data in geographic coordinates using a GPS, the above process would be the method of converting that data to a more useful format. This process is rather complex, so do not be alarmed if it does not turn out perfectly. Further detail will be provided in a later module. Acknowledgement: Screen captures of the ArcGIS GUI, pull down menus, buttons and icons are reproduced with permission as per the UK CHEST agreement and both these and trademarks (ArcGIS, ArcMap, ArcCatalog, ArcToolbox, ArcScene, ESRI) are the property of and Copyright © 2010 ESRI. This website: Copyright © 2010 Dr Christopher Green. The views expressed in this document are those of the document holder. Source.