GPS on iphone

I have TomTom on my iPhone and it works great! You are correct: with an offline-based map app you don't need any data/cellphone traffic to use it. It essentially becomes a portable GPS unit.

Hi Sue. I have recently been researching offline gps apps and I've been playing around with Sygic which seems to be a highly rated GPS app. The Italia app costs $21.99 and what I like about it is that it also offers pedestrian mode which is something I want for Venice. You might have a look at it and see if it suits your needs. They have apps for many other places besides Italy. Happy travels.

Okay, "non-techie" question. I only have the 16 GB iPhone. I'm assuming the apps that don't require data are going to be huge in size. If I get one of these, will it bog down my phone?

Off-line maps don't take up a lot of space. The various apps force you to download maps for just a city or region, so the memory storage is easy to manage.

MapsWithMe, England, only takes 275mb, Scotland's 46, France you have to break down. They all work fine.

I have a full Western Europe complete map base for TomTom, and even so it only takes 1,9 GB.

This may be a dumb question but if you turn off the cellular data part of your iphone (ie airplane mode), how does it connect with a satellite to know where you are?

Smartphones typically don't use satellites for GPS. Instead they are able to calculate your position by triangulating the distance between three nearby cell towers. I'm not 100% certain, but I believe this feature will still work if you have the data mode turned off. The calculations are all done by an internal chip which doesn't need to connect to a server. But if you turn off the data mode you will need to install an offline mapping app like Maps With Me to show where your location is.

Phones use a hierarchal matrix to determine location and refine it. They have GPS, cellular and, and wifi antennae. Wifi isn't of much interest except to know it works at limited range. Cellular is the most accurate and refines the GPS antenna and speeds up resolution by numbers real people don't understand. GPS alone will peg the location with a max error of six feet lat/lon. Any other error is the fault of the map datum or resolution. The airplane switch is stupid and has no reason to exist. It shouldn't be used except on an airplane until the NTSB/FAA unscrew themselves. Switching off cellular data kills cellular roaming as well and leaves everything else working. Using airplane mode kills wifi, the phone, and a lot more. The GPS feature will work fine with cellular data off. You might be off by an arm span and notice speed errors at Mach 3 plus. Beware.

Thanks Ed for the fine explanation, so which offline app do you like the best for Italy, so I will not have to carry my Garmin Nuvi along with me while walking around Italy? Just got back from Italy and that is what I did.

I have very specialized maps for odd-ball interests. I don't use a GPS in a city walking around. If I need anything it's a tossable paper one or the sign on a metro station. I have NavFree and MapsWithMe which both work well and would probably serve that purpose.

You're welcome Don......