Helping organize the Mobile Spatial Interaction (MSI) workshop at CHI 2007 has made me very sensitive to the usage of the term MSI. Most people see Mobile and Spatial attached to Interaction and immediately start talking about location aware applications and services. However as someone who has spent the last few years working on location-aware applications, I have always felt that MSI and location-aware apps are two slightly different classes of research. As a result I’ve been spending some time thinking about how to define MSI as well as understanding how it differs (if it differs at all) from the current of location aware applications. My definition of location aware will of course be highly biased by projects like FireEagle, ZoneTag and Zurfer)
Location
I define location aware systems as systems that know the users absolute position. The accuracy of the location will of course change as will the source input (IP, Cell tower, GPS, user sumitted), used but by definition all location-aware systems can locate the user down to some arbitrary level of accuracy. The available accuracy may vary widely from country to city to zipcode to lat/long, and typically the best possible accuracy comes from GPS receiver which has an average error rate of about 30 feet.
MSI on the other hand requires not only the users physical location but also their spatial orientation (heading at a minimum but possibly including information like tilt, height, etc…). Typically MSI also requires a greater level of location accuracy – most spatially aware systems cannot do much with city level location and generally require at least GPS level location accuracy. In many ways you can consider the MSI grade location (and orientation) to be the logical conclusion of ever improving location aware technologies.
Interaction
To me the greatest difference between location aware and MSI applications is in terms of the interactions that they can enable. A location aware application has more of a “smart†interaction where the app tailors the content based on your location. ZoneTag is an excellent example of a location aware app that suggests tags based on your current location. To the user it appears to be a smart application that just knows what the user probably wants.
MSI interaction on the other hand can go much deeper than just smart apps. Sure it would be awesome to have a version of ZoneTag that showed the tags for the object you just took a picture of but that’s the obvious and (relatively) easy part. To me the real killer app for MSI is in enabling the creation of tangible* intuitive user interfaces. Interfaces that actually interact with their physical surroundings will not only have greater adoption (due to easy learnability) but peoples innate curiosity and playfulness will make the interaction more pleasurable (if you’ve ever seen a group of tenured professors act like children at a SmartSkin table you know what I mean 
).
Magic
Ubicomp researchers have been trying to make these intuitive interfaces for years but have been hampered by the artificial nature of the sensing technology. With mobile phones becoming more powerful and increasingly including things like GPS, digital compasses, accelerometers, tilt sensors, etc… it isn’t going to be too long before every person is walking around with an MSI/Ubicomp enabling device in their pocket. If MSI researchers have their way people will no longer have to squint at tiny screens, explicit interfaces will disappear and users will directly query and interact with their real world environment. We still have a long way to go before we get there but projects like Air Messages, Point and Find, relateGateways, etc… are beginning to show how users can interact with the real world. They are opening a while new set of research questions about how people will react to such technology – I don’t know what the killer app will be but I’m pretty sure the interaction will be indistinguishable from magic.
* I am using the word tangible since even gestural MSI is situated in the physical environment.
[tags]MSI, Mobile spatial interaction, location-aware, lbs, research[/tags]
