first calculate MSA
if highest ground is terrain round up to next hundred add 1300?
or if its a strucure round up to nxt hundred add 1000?
Sounds correct. Remember that structures < 300' AGL are generally not shown on the map. That's where the difference between 1000' and 1300' comes from. (The exception is normally clearly identifyable structures that may help in navigation.)
Another method is to simply look at the sector highest obstacle elevation or sector MSA that's printed on the chart for every 1/2 degree of latitude/longitude. But manufacturers are not consistent in this respect: The ICAO chart for the UK uses the highest obstacle elevation, so you need to add 1000' to get the sector MSA, but the Jeppesen VFR charts use MSA.
hdg= true track of 085 plus var ie 5w = 090 west is best prompt!
if calculating hdg T do i take allowance for the W/V and Magnetic var or just the wind?
all my calculations seem to be off by a few degrees!!
Whatever you do, the end result should be that there's a number on your plog that you steer in the aircraft. So once in the air you try to limit the number of calculations to the minimum. No problem if you use true heading, or magnetic track as an intermediate point in your calculation, but eventually you should get magnetic heading.
Give us a full example, with wind and everything, and we'll be able to tell you where you're going wrong.
also when working out the distance of a line ive drawn from airfield to airfield do i need to start from the edge of the circle or in the middle as even this measurement can be out by half a mile!!
The center of the circle is where the airfield (or actually the "Airfield Reference Point" - marked as ARP on the approach plates) is. So what do you think?
In any case, 1/2 nm is only about 15 seconds of flight. Not enough to care.