Any good car GPS systems for use in Boston?

November 11, 2006 5:39 PM

Are there any good car GPS systems that you can buy that work well in Boston (Big Dig and all) and surrounding areas? Thanks, --spatially-confused person
posted by Malad to technology (8 comments total)

No GPS receiver will work in a tunnel. The radio signal from the satellites won't penetrate.
posted by Steven C. Den Beste at 6:17 PM on November 11, 2006

Ahh, that's true. But at least it could have highly accurate maps and judge where you are based on the entrance to the tunnel and the speed you're traveling at. I think most GPSes do that nowadays.

More importantly, though, I just need a system with highly accurate, up-to-date maps and excellent direction-creating software that take account of Boston's bizarre streets -- even if it can't give me actual location-info in a tunnel.
posted by Malad at 6:35 PM on November 11, 2006

The Garmin 7500 includes support for dead reckoning navigation. Previous DR Garmin units required professional installation so they could be legally connected to the speedometer cable (possibly also connected to the reverse gear to determine direction). The 7500 says it needs "minimal" installation, so it may just have a sensitive accelerometer.
posted by b1tr0t at 7:57 PM on November 11, 2006

I think most GPSes do that nowadays.

Unless they explicitly mention dead reckoning, assume they don't.
posted by b1tr0t at 7:58 PM on November 11, 2006

The Garmin Nuvi and the Tom Tom Go series all use dead reckoning with no external connection required. They use internal accelerometers, I believe (don't quote me there).

But they do work. Remember that car navigation systems aren't exactly "GPS" systems, in that they don't try to pinpoint you exactly on a map. Instead, they try and place you on a ROAD on the map. So the software uses the GPS signal to estimate where you are, and then places your "car" symbol on the nearest road. It pays attention to direction and speed and uses that information to improve it's guessing about which road you are on.

You can watch the "snapping" algorithm at work when you leave a road and drive in a parking lot, etc. The software will keep "snapping" your car onto the nearest road, until you get far enough away to convince it that you aren't on the road.
posted by Dunwitty at 5:07 AM on November 12, 2006

I think there are two issues for driving in cities like Boston. One is the ability to get road/construction updates quickly, and the other is the speed with which the unit barks out directions. In dense cities, and in ones without a vaguely grid-like structure, your GPS really has to let you know it's this turn! not that one in 10ft.

This review of four GPS units may help you out. It looks like two of them give real-time traffic updates (the Garmin and Cobra), and I don't know how they'd do that without maps that are updated frequently, too. I have an older Garmin (5, I think) that doesn't update without connection to a PC (which is a drag now that I'm on a mac) and which has a response-time slightly too slow for some dense cities. For instance, I've used it in Grenada and London and it has a hard time syncing quickly enough. I have learned to anticipate or guage the lag time and can compensate for it, so otherwise I'm very happy with the unit and have gotten a lot of use out of it.

BTW, I live in Boston (ok, Cambridge), and use it here frequently, too.
posted by cocoagirl at 6:33 AM on November 12, 2006

Spatially confused is a constant state in Boston. I have been here 1 yr 3 months, and I use a Pocket PC (Dell Axim) in tandem with a Holux GPSlim236 and Mapopolis maps. Yes, the GPS cuts out under tunnels, but then it works again once you're out. And no system will have things completely updated since the changes happen daily, but I don't think I would have lasted in Boston as long as I have without my GPS. It's a necessity. Boston signage is terrible. It's an insider's town.
posted by abbyladybug at 11:41 AM on November 12, 2006

In terms of the part of your question relating to data that's so up-to-date that it stays current with major, ongoing road restructuring like the Big Dig, I think that the answer is no, for now. As many different devices as there are, I think that there are only two main companies that supply their map data, NAVTEQ and TeleAtlas. There is free data available from governmental sources and perhaps some smaller players, but those are the big two. They update their data constantly, but there's a long lag -- at least several months -- before it's incorporated into new devices. I know that NAVTEQ, at least, welcomes user-provided corrections, and they can let you know whether the correction is already in their database, but they can't instantly make it show up on your GPS device.

The traffic service is up-to-date, with construction notices and flow information, but it doesn't reconfigure the maps themselves. TomTom's US traffic is currently down, has been for weeks, and is expected to be for weeks more.
posted by daisyace at 3:47 PM on November 12, 2006