I thought it would be fun to take a different angle on the virtual globe competition and look at the content and data made available by two of the players - Google and ESRI. From a technical perspective I think most would agree that ArcGIS explorer is pale emulation of Google Earth especially when it comes to user experience. I’ll put aside my gripes around difficulty in set up and version updates with Explorer and focus on content. The ESRI supporters have made the argument that ArcGIS Explorer is about access to GIS content and has a different mission than Google Earth. Actually, I would say the missions (exposing geographic data to larger audiences) are the same but the approaches are much different.

I’ll assume that some day ESRI will nail the technical side of Explorer, and look a little further down the road - to the content available for Google and ESRI’s thick client applications and how easy it is to access. As the GeoWeb evolves and we’ve rendered ever more amazing three dimensional worlds I think an increasing premium is going to be on the scope of data and content that can be delivered to these applications.

So where do the two ends of the GeoWeb spectrum sit on the topic? From my observations pretty far apart. For practical purposes I’ll break the comparison into four topics 1) data formats 2) data sources 3) data search and 4) data packaging

Data Formats

This is one category where ArcGIS Explorer ups Google Earth cleanly. Explorer allows you to load ArcGIS Explorer files (.nmf why they felt the need to create another proprietary file format that works with nothing else is beyond me), servers (WMS, IMS, file server), geodatabases, shapefile, raster, and KML. This is an impressive list, although a little bit less impressive when you consider that half are open standards KML, WMS and raster and the others are really ESRI proprietary formats at the end of the day. On the upside the raster support is quite extensive (30 or so different formats), although they require a spatial reference file.

On the Google side you have KML and KMZ (once proprietary now turned over to the OGC - jury is still out on how open it will be) for the free version of Google Earth, and within the free Google Earth 3-D warehouse support for SketchUp “.skp” and COLLADA “.dae”. In Google Earth Pro and Enterprise versions there is vector support for ESRI shapefile and MapInfo .tab, and for imagery support for TIFF (.tif), including GeoTiff, National Imagery Transmission Format (.ntf), Erdas Imagine Images (.img), Atlantis MFF Raster (.hdr), PCIDSK Database File (.pix), Portable Pixmap Format (.pnm), Device Independent Bitmap (.bmp). While this is an extensive list you have to pay to get the file support, in ArcGIS Explorer the support is currently free, so ESRI does have a distinct edge in the category.

Data Sources

In addition to supporting different file formats there is also baked in content for both applications. For Explorer you can access ArcGIS Online directly through the file server option, which allows you to access a file directory of cotnent. A second option is you can access the “Resource Center” website through the help tab, where you can download content in the .nmf file format. The “Resource Center” is definitely the more user friendly of the two with a nice user interface categorizing content into useful categories like, “imagery, street, physical features”.

On the downside the content is very limited - twenty four layers supplied by ESRI and four contributed by the community. ArcGIS Online has more content, but was a pain in the ass to access. You have to get a user name and password from ESRI, read through the incorrect direction to access it, then you get a list of UNIX style titles with abbreviations and underscores, like UNEP_WCMC_WDPA2006_2D. Not exactly user friendly, but you do get close to fifty additional layers of data once you jump through the hoops.

In Google Earth there are two sources of baked in data from the application, “Layers” including (terrain, geoweb, roads, traffic, 3-building, borders and labels, gallery, global awareness, and places of interest) and the ability to search for businesses. You can also click the “help” tab and be taken to the Google Earth Community web page. On the Google Earth Community page site alone there are 638,213 KML or KMZ files.

While finding this content (they are all file attachments to bulletin board posts) is pretty clunky and often frustrating, it is a LOT of content. Especially when you compare it to the four user generated files on the ESRI equivalent. The quality and source of this content/data varies wildly, and it is difficult to tell what is good and what is bad, but the potential is there. Actually the metadata support for both is pretty sparse. This is ESRI’s metadata for a .nmf imagery layer from the “Resource Center”:

“Displays satellite and aerial imagery at a 15m minimum resolution worldwide, and 1m resolution for the U.S. World boundaries, place names, and transportation layers are also included. Use this map to view man-made and natural features, or as a base map for overlaying associated data layers.”

For an ArcGIS Online layer this:

Layer Name: Imagery
Layer Source: ArcGIS Globe Service Layer
Layer Type: Draped
URL: http://services.arcgisonline.com/v92
Service: I3_Imagery_Prime_World
Sub Service: Imagery
LOD Tile Fetch: True
Hidden: False

Neither super useful.

Data Search

Neither application directly supports data search, but both have communities or services built around them that do. On the ESRI side there is a huge number of geospatial data repositories that have shapefiles in them and the search capabilities of them vary widely. Probably the largest is the Geospatial One-Stop that has a connection to most Federal geospatial data. Although in reality it is more often access to the metadata than the data itself. Still a large amount of content that could be conceivably viewed in ArcGIS Explorer, although largely disconnected in a large number of different repositories.

Google Earth has not only a good number of community aggregators like the official GE Community site above and unofficial like Mapufacture, GE Library and GLayers, but also the ability to search all KML files indexed on the web. I’ve heard numbers north of 10 million KML files indexed by this approach, but have nothing official. One way to search this content base is to type filetype:kml

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