Do airline pilots really do this???
Pre GPS, the aircraft position/gate was entered into the IRS. The system can actually calculate it's latitude pretty quickly due to the precession rate but it has no idea of longitude until you tell it. Many airports have the stand lat/long on a big board in front of you so you can check. The Aerad charts have all stand co-ordinates listed so you can enter/check your position.
When you put the departure runway into the Boeing/Honeywell FMC it knew the threshold co-ordinates from it's database (which you then offset by x hundred meters if you planned an intersection departure). When you advanced the thrust levers to take off, the position was updated accurately as the FMC assumed you were taking off from the actual runway position it "knew".
Entering long string lat/longs is quite common for new waypoints, positions you need to reach that are not in the database (eg composite tracks over the Atlantic). Fortunately most are just whole numbers but there are some positions that are similar to "N2530.0 W08600.0".
With GPS aircraft, they still run IRS systems but the GPS provides another source of position information along with the INS position, DME/DME, VOR/DME and VOR/VOR positions (with the obvious accuracy improvement). The aircraft position on the gate is
always checked prior to departure as part of the FMC set up.
In the example below the "SET IRS" position box would be blank/dashed until you entered the position (simply just a copy/paste from the stored database gate position above it).
PS Thanks to
The Boeing 737 Technical Site for loan of the image!