1. All projectiles were fired from Gaza; the Israeli blocking of traffic and movement between Gaza and the West Bank, and Israel's partial military control of the West Bank versus it's lack of direct control of Gaza have ensured that mortars and rockets don't get fired from the West Bank.
2. The inexorable rise from 2002-2004 reflects growing technical ability, not any change in ideology or political will. The steep drop in 2005 was the conscious decision of all Palestinian factions not to aggravate the Israelis as they prepared to disengage from Gaza. It would have been irrational to shoot at Israelis as they were about to leave,especially as some Israelis thought the leaving was a poor idea, and one didn't wish to strengthen their hand.
3. I do not know why 2006 is a bit lower than 2004, since by then the Israelis had left Gaza and there was no reason left for Palestinian restraint, but by 2007 they'd gotten over it and were back to the previous model: growing technical ability means more projectiles.
4. The total number of projectiles in 2009 mostly reflect the mass firing of everything Hamas had during the fighting in January. After that only very few projectiles were shot. (This mostly holds, so far, for 2010 also).
5. The Israeli operation in Gaza in January 2009 was demonstrably proportional: it achieved its goal, and then stopped.