Mapping using Google Earth

Google Earth is a free computer program that enables you to mark points and outline areas on a global map that is based on satellite imagery. You must be online in order to use it, and a faster connection helps.

Download the program from here: http://earth.google.com/download-earth.html

The Google Earth User Guide can be accessed from the Help menu in Google Earth. Exploring it can give you some basic tips and skills for using the program, finding places, navigating, and so on. The following sections review how to set and edit a placemark or point, how to draw and edit a polygon or area, and how to send the resulting .kmz files to other people.

Creating a placemark

In Google Earth, navigate to where you want the placemark. Click the Add Placemark button at the top of your screen (with the yellow pushpin).

1. A window will appear, which you can move out of the way with your mouse, in which you can enter name, coordinates, style information, the height of the view, and any other info in the description window.

2. A pushpin will appear in the center of the 3D viewer, with a flashing box around it. You can position the pushpin with your mouse.

3. When you click OK on the window, the placemark is saved in your My Places folder (left hand side of the screen). Subsequently, you can navigate to this placemark by double-clicking on it. You can choose to reveal it or hide it using its checkmark box.

4. To edit the placemark after you have saved it, you can right click on it in Windows/Linux and choose Properties. This opens the window, where you can change its location, information, view, altitude and description. Click OK to save.

Creating and editing a polygon or area

To create a polygon or area, navigate so that the entire area of your polygon is in view. Click the Add Polygon icon to the right of the Add Placemark icon at the top of the screen.

1. A window will appear as for a placemark. You may add title, and choose the style of the outline and fill under the Style, Color tab. It may be easiest to draw accurate polygons without concealing the area within, so choose outline only. You can change these properties later.

2. In the 3D viewer for the map, your mouse pointer is a square box with centering marks. You can create your polygon in two ways: click and release on the corners, or click and drag around your desired boundary. If you do the latter, the mouse pointer will change to an upward pointing arrow, and generate a lot of perimeter points.

3. As soon as 3 points are designated, you have a polygon. You can continue to add perimeter points. You can edit points by moving your mouse over them until it becomes a hand pointer, then moving them. If you click on a point, it is selected (it is a different color than the others), and you can delete it using the Backspace key.

4. When you delete a point, the previous placed point is then selected. By using the backspace key repeatedly, you can undo a string of points in the reverse order that they have been placed.

5. The order of the points is important. To add points to an existing perimeter, you must first select the point that is BEFORE the point you would like to add. If you are going clockwise, for example, and you have points at noon, 3, 6, and 9 o'clock positions, you must select the 9 o'clock point before you place the 10 o'clock point, or else you will create a star-like formation with crossing boundaries.

Folders can contain multiple placemarks and polygons

It is a great idea to organize your mapping by the use of folders. To add a folder, Ctrl+Shift+N in Windows, or choose Add, Folder from the menu. Once your folder is created, you can add items to it by dragging them.

Sharing files

Mapping information is stored in .kml files (Keyhole Markup Language, a simple text format based on the XML standard) or in compressed .kmz files. You can email these files easily by right clicking a folder, polygon, or placemark in Windows and choosing Email. This will email a .kmz file. If the recipient has Google Earth installed, clicking on a .kmz file should open Google Earth, with the file in the user's Temporary Places folder. On closing Google Earth, the user has the choice whether to save that file or not.

Calculating areas

In Google Earth it is not possible to calculate areas. However there is a free tool called GE-Path that can calculate areas from .kml files. Download it here: http://www.sgrillo.net/googleearth/gepath.htm

If you wish to calculate areas of pastures for example, you will want to map them as polygons rather than merely making lines or paths for your pasture divisions.

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