When using a map and compass for navigation, do I use declination or not?

Do you mean magnetic deviation?

This article also discusses the mag. declination issue; they are intertwined.

Paralysis of analysis I think. But over distance it could be disastrous.

Depending on how far off your true north is from your magnetic north, in general, yes, you need to take declination into account. The farther off you are, the more important it is.

What kind of maps will you be using? It’s been decades since I used USGS maps myself, and I don’t recall if they have notations on the maps themselves about local deviation. But it’s the kind of thing that you can check yourself if you sight from one charted landmark to another, then compare your compass reading to the charted / predicted value. If you have the map (or one like it) in hand prior to the start of the event, then you can take care of the check before you even start the quest.

I’ve never done orienteering. I’ll have to suggest that to our Adventurer’s Meetup group. It sounds like fun.

I hope this helps.

Yes, you need to consider it. There is an indicator at the bottom of a topo map from the USGS that shows what the declination is for that quadrangle. If you have a well run orienteering competition, without it you’ll be off in your calculation.

It depends on how you’re using the map. If you’re going off of two distant points, like mountain peaks, then no, you don’t need declination—all you need to do is triangulate. If you’re only going off of only one distant point and your compass, then yes, you’ll need to put in the declinatinon into the compass. Every USGS map has a declination written on it.