Thursday, December 1, 2011

Google Latitude export ... One day only ... And no wonder.

Google Latitude used to let you export a date range of your location history to view in Google Earth or other maps.  Now you can only see a day at a time.  This post explores some possible reasons why.  (Another post shows the workaround.)  I don't think it's about data download size.  It's about not confusing the user.


Google Latitude seems to offer a great way to do geospatial analytics on yourself.  But mostly, Google guesses what you want to know about yourself and does the analytics for you.  Click the Latitude Dashboard to get Google's analysis of your movements:





But what if you want to analyze your movements differently?  How about just seeing your locations over time on the map? Click a calendar date and see a map of your locations:




But that's it. Only one day at a time.  

How about exporting the last 6 months of your locations so you can do some real geospatial analysis?  In the past, you could export a data range to KML to view in Google Earth.  But Google decided a few months ago to remove that option, and now you can only export a day at a time.  This caused some anger among users.  (Users found a workaround described here.  I offer it as a visual tutorial in another post.)

If you work around the limitation and get lots of locations into KML and Google Earth, here is the mess you'll see:




No wonder Google doesn't want to give you all this data.

I expected to see more clearly identifiable tracks.  But there are two problems:  

First, Latitude is taking my locations not just from GPS, but also from cell towers.  Like the tower at the center of the San Mateo Bridge over San Francisco Bay.  And along El Camino Real west and north of Redwood City.  

What gives the impression of false tracks is that the KML is drawing lines between time-sequential points (including widely spaced cell towers).  Often there aren't enough data points to create a useful track.  (I don't know enough about KML to switch this off and look at just the points without the connectors.)

Besides misleading connectors between points, the zoomed out view illustrates another problem:




I know I didn't visit Florida or Hawaii in this time window (although I wish I had.)  What's the problem?  

Google suggests the answer in their disclaimer about location accuracy and source data.  When GPS is turned off or not available, Latitude uses wifi (not an issue here) or cell tower ID to get your location.  Even when GPS is turned one, "When Latitude is running in the background, it will default to cell ID (cell tower) location on most phones to preserve your battery life."

Another note in the disclaimer suggests why cell tower data can invent my "visits" to Florida and Hawaii: 


"Cell ID (cell tower) accuracy depends on ... available data in Google's cell ID (cell tower) location database."  The phone doesn't give the cell tower location to Latitude; it just gives the cell tower ID number.  Google has to get the lat/long by looking up the cell tower ID in their database.


What they don't explicitly say is that many of their cell ID records may be not only inaccurate, but totally bogus.  So, your cellphone pings Sprint tower 000328282.  And Google's cell tower database has that listed in Plains, Georgia -- not San Francisco, where you really are.


Limiting your location view to one day at a time would make outliers stand out, so they are easily disregarded.  Maybe this generates fewer complaints from Latitude users.


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