I planned the trip to very north location - Svalbard/Spitzbergen islands which are about 700km north from the Nordcap in Norway.
I heard, that flying in such regions may be problematic because of the compass abnormality.
Somebody know something about that?

It would be a good idea to read this thread and the one linked in the first post: http://forum.dji.com/thread-94380-1-1.html

I have never flown there, but I think you will be OK.  

• The GPS will have poor accuracy and you should avoid going the north side of a hill or building since all the satellites are low in the southern sky.
• The compass may have a few problems, especially if there is a solar storm but I think it will work OK'ish.
• Keep the aircraft high enough that it can't hit anyone or anything since the GPS inaccuracy may cause sudden uncontrolled movements.
• You may have to switch to using Atti mode if it becomes uncontrollable, so only fly in good conditions and get some Atti practice in first.
• Try and give the downward vision cameras something easy to see with decent light so that it does not have to use the inaccurate GPS to hold position.
• Remember that RTH needs GPS to work, if you need to use Atti to keep control then you must not press RTH.  Set the RTH height very high so that it has a better GPS signal, it will also help you to take control back and use Atti if necessary.
  

It may be a good idea not to calibrate the compass while there since getting an accurate calibration may be difficult, not sure about this?

Nigel_ Posted at 2017-5-2 23:42
It would be a good idea to read this thread and the one linked in the first post: http://forum.dji.com/thread-94380-1-1.html

I have never flown there, but I think you will be OK.  

"Try and give the downward vision cameras something easy to see with decent light so that it does not have to use the inaccurate GPS to hold position."

Since the VPS has a range of 3 metres fir the P3 series and 10 metres for the P4 series, it's not going to be much use for most flying.

Labroides Posted at 2017-5-3 00:05
"Try and give the downward vision cameras something easy to see with decent light so that it does not have to use the inaccurate GPS to hold position."

Since the VPS has a range of 3 metres fir the P3 series and 10 metres for the P4 series, it's not going to be much use for most flying.

It's probably irrelevant to the OP since he appears to have P3, however for others who might read the thread...

The ultrasonic sensors on the P4 normally have a range of between 8 and 15 meters depending on the reflectivity of the ground surface, they are used for measuring actual height (not barometric height) and the height is often called VPS (Vision Positioning System) height.  

The downward optical sensors would work at any height for horizontal hold as long as they can see the ground, so not above the clouds!   I've never seen anything which suggests that they are turned off when the ultrasonic sensors go out of range, it seems silly to turn them off at only 10 meters when they could avoid a crash into a 100m tall building!   Does anyone know for sure if they are turned off at any specific height?