In the following fotograph you see a raspberry pi with a wifi-dongle and gps attached to it. Any wifi stick will work as long as it is supported by Linux.
The program is then started from /etc/rc.local as follows:
/usr/bin/screen -d -m -S 'owsc' /usr/local/bin/owsc.sh
The /usr/local/bin/owsc.sh script looks like this:
# this loop is required as anything connected to usb on a
# raspberry pi behaves a bit flaky
/sbin/ifconfig wlan0 up
/usr/local/bin/ows-collector -w wlan0 -g /dev/ttyUSB0 -d /root/wifi-data.db -l /var/log/ows.log
Then connected the device to a battery and starting cycling through your neighbourhood! When you get home, connect the raspberry pi to ethernet, retrieve the /root/wifi-data.db data and do a clean shutdown.
The /root/wifi-data.db file can then be processed (see included readme.txt) and uploaded to the OpenWLANMap website.
Example result at OpenWLANMap: