Google Earth as a Browser and Authoring Tool for the GeoWeb

The world wide web is a means of encoding information and tying documents together with references to other documents. In ordinary web pages the references are addressed with < href="http://en.wikipedia.org/wiki/Uniform_Resource_Locator">Uniform Resource Locators (URLs). In the GeoWeb, our information may incorporate and be referenced by URLs, but our content is also referenced spatially and potentially temporally. The neat thing about spatial references is that information encoded this way may be linked to other information about the same location. Linking through URLs is intentional, static and precise. Linking infomration in a shared referencing scheme like spatial coordinates is more flexible, unpredictable. Spatial referencing in the GeoWeb is one aspect of the development of a web where information is linked together in a referencing system based on the Meaning also known as The Semantic Web. This page will be an introduction to encoding information for the GeoWeb using Google Earth.

Download the Sample Data

Recommended Reading

Creating Coherent Collections

In this tutorial we will explore the elements of content creation in Google Earth. Mostly, we will refer to the google earth documentation to learn the nuts and bolts of creating content. But we are going to add a twist: we are going to pay close attention to the way that the elements relate to each other. Beginning with a good structure will help us to develop information about many discrete resources in such a way that the collective effort of compiling individual resources comes together as a coherent collection that can grow in a rational way. In tis tutorial we well discuss using Google Earth as a framework for adding spatial and temporal coherence to various resources that we will find on the greater web. For your convenience, the examples we will use are included in the sample dataset linked above.

Google Earth as a GeoWeb Browser

First, lets explore Google Earth as a Browser for the GeoWeb. First, type an address or the name of a place into the Search panel. Google Earth consults a geographical thesaurus known as a Gazetteer to find synonyms for your ad-hoc spatial reference. The choices that appear in the search panel include synonyms that have explicit geographic coordinates. We are looking for information on the area surrounding City Hall Plaza, Boston.

Now go to the Places panel. This is a collection of content that Google curates. This is an easty way to discover information related to our area of interest. If you open up the Gallery group, and turn on You Tube you will be able to find lots of youtube videos related to City Hall Plaza. Click the YouTube icon directly in the center of City Hall. Open this in YouTube and from here you will discover lots of other resources related to future visions for City Hall Plaza! Explore some of the other curated content in the Places Panel. Turn on the Time Slider to view some historic imagery of Government Center.


Google Earth as a Frameork for Georeferncing Content

Google Earth is a browser and a search/discovery tool, but it can also be used for creating and georeferencing content. In the next sequence of steps you will learn how to create Folders, Placemarks, Polygons and other geometry, Ground Overlays, Georeferenced Photos, and 3D Models. To learn these techniques, you should just read the Google Earth User Guide. This tutorial will suggest some content that will place these tasks into the context of a study of the history of Government Center, which was formerly a neighborhood known as Scollay Square, which was destroyed in 1961 or so. We will use this tutorial as a means of describing how the GeoWeb can be used as a framework for understanding the past and future of this place.


Create a Folder and Some Geometry

  1. Follow the instructions in Creating and Organizing Folders to create a folder. Set the view so that when you click on this folder it will return you to Government Center. Write a description of your project in the Folder's Description properties.
  2. Follow the instructions for Creating a New Placemark to mark the position of some point of interest with one of the stock icons. Make the icon float 50 meters above the spot, connected to the ground with a green leader line. Use a meaningful title for your placemark. Experiment with icons.
  3. Lets follow the instructions for Drawing Paths and Polygons to create a new polygon that describes the shape of a building. Adjust the Altitude settings to cause this polygon to extrude. Write a short description of your building in its Description properties.
  4. Drag your polygon and your placemark into your folder.
  5. Create a folder for your work on the computer's hard drive. If you haven't already, unzip the sample dataset to your C:\temp folder and make your own folder inside the Scollay Square Folder, next to mine. Do not use spaces in your folder names. Inside your folder, make a folder named resources. This will be where you put your KML files and other resources.
  6. Export your folder to a KML File

Geolocate a Scanned Map

The Now lets bring together some imagery about the deep history of the place. We can find lots of information about old Scollay Square on the web. Now lets demonstrate how we can add structure and coherence to some of this information using spatial references. An important thing to keep in mind while doing this is that when we pull data out of the web to increase understanding we want to be careful to collect information about the resources that we gather. This is important for a couple of reasons: first, as a matter of scholarship, we want to be able to reference the locations where we found resources so that we, or someone else can easily return to that source to find out more. Similarly, there will be information about the Primary Source for the resources we collect that is essential for understanding how the resource relates to the place and time where it was collected. Therefore, when we gather information from the web, we will look at vaqrious ways for saving informaion, some of which we will put into the Description tag for the KML files that we create.

There are many places to find old maps on the web. YOu can find many of these on the page, Sources of Geographic Images. I highly recommend finding very derailed old maps at the Sanborn Mp Collection. IN our example will take the Rand Mcnally 1903 map from the David Rumsey Collection. This map has an instet of Downtown Boston that we are particularly interested in, so we downloaded the image and cropped out the corner using an image editor, like Photoshop. Tomake this tutorial easier, I include the Cropped Image here.


Saving and Georefeencing an Old Map

  1. Visit the Rand Mcnally 1903 map at the David Rumsey Collection.
  2. Notice the detailed documentation, also known as metadata on the left side of the screen. Also note the Export button above the map.
  3. To make things easier, just Click here to download the cropped image.
  4. You are going to save several things related to this resource, so create a folder named RandMcNally1903 in your resources folder, and save the image in there.
  5. Now open a new WordPad file (or use your favorite text editor) and copy and paster the metadata frm the rmseay collection in there. While you are at the web page, copy and paset the URL for the resource at the top of your text file, and finally write the date a which you accessed the map.
  6. Save this documentation as a plain text file into the folder with the image.
  7. Now use Google Earth to register the old map into its approximate location on the earth. Follow the instructions at Creating Image Overlays in the Google Earth User Gude.
  8. Copy and paste some of the critical information about the Primary Source and the Date of the original map as well as the location where you found it published into the descriptive text for the image overlay.
  9. Save your image overlay as a KML not KMZ file into the folder with the image and its metadata.

A Note about KML vs KMZ

You have seen how the Save Place As dialog has an option to save your creations as KML files or as KMZ files. KML files are plain text, like HTML files are. KMZ files are actually zipped archives that contain their own mini filesystem. A KMZ file allows you to package binary files, like JPG images with KML. This makes a handy capsule that is easy to pass around. This can be handy, just like packaging an illustrator document with all the various linked resources that it contains. However, when we are developing large collections of diverse resources it is better to keep our KML files and resources organized for ourselves iinmost cases. We will talk more about this later. For now, we will experiment with KMZ just to see how it works.


Save and Explore a KMZ file

  1. Save your georeferenced map as a KMZ file in the c:\temp folder.
  2. Set your windows folder view options to show extensions for known file types
  3. Change the .kmz suffix of your file to .zip
  4. Double-click on your zip file to inspect the mini file system inside!

It is possible to save complexes of folders and geometry and images as single KMZ files. This is very convenient in terms of packaging data, but it can become very complicated and frustrating to try to use KMZ as a means of organizing lots of data and metadata. So for now, we will stick with using KML.

Downloading a 3D model From the 3d Warehouse

Google has a big collection of 3d models. Tons of these can be viewed if you turn on the 3D buildings layer in Google Earth. Much of this model is not downloadable, but there are specific models that have been contributed by users to the Google 3d Warehouse. These models are not KML, but another XML-Based format known as COLLADA. We will learn a lot more about COLLADA later. For now, we will remark that COLLADA models combine geometry and images together in zip archives just like KMZ. And these may, in turn be embedded into a KMZ files to that can georeferenced and viewed in context in Google Earth. Because we find these resources as KMZ files, we will save these resources as-is in our compilation.

The Boston Custom House Tower is a landmark building that can be used as a reference for georeferencing photos, etc. So we will download a model of the Custom House Tower an add it to our collection. We want to preserve the original model as we found it, so we will resist the temptation to edit the KMZ file. Instead, we will create a Network Link which will give us a simple way to reference the model with a simple KML file to which we can add and save important source documentation.


Collect a Landmark Building and a Network Link

  1. Turn on the 3D buildings in Google Earth's Layers panel.
  2. Find the Custom House Tower -- an pointy tower to the East of City Hall.
  3. Mouse over the tower, notice that it has a blue highlight. That means that there is a downloadable model. Click it to learn more.
  4. From the menu underneath the image of the model in Google 3d Warehouse, see that you can download a KMZ file. Do this, and create a new folder for it in your own resources folder.
  5. Also save whatever metadata about the source and the subject model that you can gather from the we page, and save this as a text file, along with the URL as we did before.
  6. Take a look at your new model in Google Earth!
  7. Now, you see that the KMZ file does not have any useful metadata in its description. We want to add this using a network Link.
  8. Right-click on the Temporary Places element in your My Places panel and choose New>Network Link. IN the properties, click browse to find your custom House Tower KMZ.
  9. Paste useful metadata into the description.
  10. Save this as a KML file into the folder with the original file.

Georeferencing a Photo

As you can see, we are gathering a collecion of diverse resources! The compilation itself provies important context for understanding how things relate to one another. Such a collection will yieldEmergent information that exists in the compilation but not in any of the inmdividual resources! This will hit home as we take the project one step further in adding a historic photograph.

When you think about it all photographs are historic photos. And in most cases, photographs may all be referenced according to the place and time that they were collected. We can see that the popular photosharing site, Flickr has a means of georeferencing the photos that people share. As of now, they don;t seem to be that concerned about managing the temporal references, but I suppose that will change. We did a Flickr Search for Scollay Square and discovered a lot of old photos. This search helped us to discover an amazing collection of photos at MITs Library taken by the noted urban Designer Kevin Lynch. THese photos have extensive metadata.

We will use clues in the photo's metadata and our old map and our landmark model as a means of figuring out exactly where the photos were taken. Once georeferenced, these photos will tell us much more about what Scollay Square was like, and how elements of the old square relate to the current state of Government Center. What if Kevin Lynch had Google Earth???


Georeference a Photo

  1. Find a good photo that has a distinguishable landmark. Try this one.
  2. Copy the smaller of the two photos to a new folder in your resources folder. Give the folder a name that reflects the title of the photo but remember-- No Spaces in File Names!
  3. Also cut and paste some metadata into a text file as before.
  4. To figure out where this photo was taken, it will be helpful to see the reference to the Bodoin Square Garage in the description. You can find Bowdoin square on the western edge of our old map.
  5. Follow the procedures at Placing a Photo To georeference the photo.
  6. Copy metadata into the Description for your photo.
  7. Save your work as a KML file in the folder with the photo.

Putting it All Together with an Index.

We now have a collection of resources that can keep growing and growing. One nice thing about all of this is that with our folder architecture, each of us can go to work collecting and georeferencing information in our own resources folders, and if we have a shared place to put these, we can all actively benefit from the others' work and the image of old Scollay Square will become cleared as we fit the pieces together!

THe individual resource folders are particles in a larger model. We can use a folder of network links to serve as an index for the work that each of us is doing. Ten it will be easy to compile everyone's work into one big 3d model. Fo rthe last setp in this tutorial we will create this index for our personal collection.


Create your Index

  1. Create a new folder in Google Earth
  2. Put your name in the Title of this folder and enter some information about why you are collecting these data and the date of this activity.
  3. IN this folder add three network links that reference the resources in each of their folders.
  4. Save your folder in your folder outside of the resources folder.


Now go and find another historic map and a photograph and bring themn together in a georeferenced collection with an index. We will then combine our work in one master index file foro the Scollay Square project!