Q:

having trouble looking for the right gps

I'm looking for a GPS for a small class project. We want the smallest GPS possible and all we really need it to do is to give us longitude and latitude values when we poll it.
I tried looking at sparkfun, but since we haven't really worked with this type of hardware before, it's hard to know which kind we really want/what parts we need.
What We Need: 

smallest possible
longest battery life
only need long and lat
able to be polled from some other device such as a mobile app or website

Thanks!

A:

there are two paths to this, one is just get a bluetooth receiver, you will be able to poll it from a mobile phone or whatever.  going to likely be as big as the phone, have the battery inside, etc.  not sure how long it will last on one charge.
There are other solutions designed for putting in packages being shipped, better battery life, but their goal is as data loggers and not necessarily something you can cable up and poll and likely not wireless if that is what you are after.
Now if you want to build your own, and you already went to sparkfun, here is another path.
I know that leaving links in an answer at SO is bad...This was longer than a comment and will add some more info...
You want small you can go with this
https://www.sparkfun.com/products/11571
It is a GP-635T gps receiver, if you look at the picture it really is around the size of a quarter.  50 channel.  Point it up the way they tell you, antenna is built in, just power it and it works.
You will need to hook up to it.  It is the serial version not usb, in either case you need a cable like this.
https://www.sparkfun.com/products/10361
This link is to a cable with 6 or 8 inch pigtails, the gps receiver comes on a board with a not so uncommon connector on it, this cable allows you get at those connections, you only need three.
The datasheet on the sparkfun page or probably just search for the part number, you need to look at the UART TTL pinouts not the usb pinouts.  Yo uneed 3.3 to 5.5volts to power it pin 2, pin 1 is ground.  then pin 3 is txa serial out.  This is where you get your data.
these are various solutions that will work
https://www.sparkfun.com/products/9873
https://www.sparkfun.com/products/718
http://jim.sh/ftx/
some soldering may be required.  The above links are various solutions between $10 and $15 for ftdi usb to serial/uart break out boards.  These will include 3.3v and ground and the rx pin is the receiver for the ftdi uart, you tie that to txa on the gps unit. 
What you may not know and may be interested in is that almost universally gps units do their math magic and come up with the various items time, position (2d or 3d), speed, etc.  And they output this data in a serial manner.  search for NMEA or NMEA-0183.  The data sheet for this and any other should give an indication of the default data rate (4800, 9600, 19200, etc baud) and what messages are sent.  sometimes you can change the baud rate, sometimes you cant.  The ftdi chips/boards are very flexible use a usb cable to plug in the board to a computer, configure your software or a dumb terminal program like minicom or hyperterm or teraterm or whatever (no parity, no hardware flow control) and the messages will appear usually once a second.  Whether it is your car navigation, handheld gps, whatever, buried inside is some flavor of gps reciever (sparkfun will give you an indication of just how many different flavors there are and their selection is just scratching the surface) that outputs serial and the software in that unit is receiving that serial data and then doing its thing (mapping, navigating, etc).   As with modems back in the day the ones you find in your cell phone might have some of the software/math done by the main processor in the phone to save on money, these libraries are not generally available, when you make the deal to buy thousands or millions of units they allow you to pay for the software to go with it along with your signature on a bunch of legal documents.  I assume this is the case, that is how the ones in phones are down to $10 or so where these fully contained solutions are usually $50 to $100 in single quantities and likely not a lot cheaper in quantity.
Once powered, even if it says X number of seconds hot or cold to lock it doesnt always take that, sometimes if it has to search it may still take a while, the less metal you have around (like being in a building or the center of a car) the worse it is to the point it may not lock.  
if you have an older garmin street pilot (that is otherwise dead I would hate to kill one of those if it is working) you can rip it apart and likely find a sirf III or other module in there, likely a 5V not 3.3 (there are 5V ftdi based breakout usb to serial. the microftx is both 5v and 3.3, note the gps receiver linked above is also 5v or 3.3)  googling will be required to figure out the pinout and such, and soldering might or might not be a challenge.
you can also find old etrex or other handhelds on ebay or wherever (that work!) and for $15 or so get a serial cable, well then you need a serial to usb likely which will also need a level shifter like a max232, you dont plug this right into a ftdi break out board, it will fry it.  newer ones have usb and  you can power the unit from the usb and likely see the nmea data over the usb as well.
Most of the stuff you see on sparkfun in the gps area is going to be related to these various brands and models of gps recivers that output nmea data over serial.  some are 5V some are 3.3, many do not have antennas and you have to buy those separately (and get the right kind, one that plugs into the connector provided, etc).  I have a number of these items and they all work just fine, some do better than others around buildings or in trees, etc.  Around sparkfun you will also find lipo battery solutions and bluetooth or xbee or other wireless solutions, very quickly if you need wireless, I think you will find just buying an off the shelf solution is best.  I have had my eye on the garmin bluetooth thing google
Garmin GLO Portable GPS and GLONASS Receiver
it is about $99.  I have not pulled the trigger yet so I dont know how good or bad it is, the el cheapo brands just look cheap.
Of course, a smart phone has both wireless and a gps and you can get a lot of used phones for cheap on ebay.  Ios and android.  You could "just write an android app" and put it on the phone and use one of the wireless interfaces built into the phone.  It will chew through the battery yes, how fast?  who knows.

