CLIMBED TO 3000' VERSUS 2000' ON THE MDW CANAL 3 SID.

Narrative

WE WERE CLRED CANAL 3 DEP OFF MIDWAY RWY 31L. F/O DIALED IN 3000' IN OUR ALT ALERT COUNTER. ON TKOF BRIEF I DOUBLECHKED DEP PLATE ALT AND VERIFIED 3000' ASSUMING THAT ALT WAS ASSIGNED BY CLRNC DELIVERY. AFTER TKOF IN A CLBING RIGHTHAND TURN TO THE HDG ASSIGNED BY THE TWR; DEP CTL TOLD US TO DSND FROM 2500' BACK DOWN TO 2000'. AFTER LATER DISCUSSING THE SITUATION ON THE TELEPHONE WITH DEP'S SUPVR I AGREED THAT WE SHOULD HAVE ONLY CLBED TO 2000' AT THAT POINT. TWO PROB AREAS EXIST AT MIDWAY ARPT ASSOCIATED WITH DEPS: 1) DEPENDING ON WHETHER YOU ARE GIVEN CANAL 3 OR MIDWAY 3 DEP YOU MAY CLB TO 2000' OR 3000' AND OFTEN TIMES ON THE TKOF ROLL MIDWAY TWR WILL CHANGE THE ALT CLRNC FROM ONE TO ANOTHER. SOLUTION: ASSIGN ONLY 1 ALT TO CLB TO (PROBABLY 2000') WHEN DEPARTING MIDWAY ARPT. THEN AFTER TALKING TO DEP CTL ALLOW THEM TO CLEAR TO CLB HIGHER. THERE ALWAYS SEEMS TO BE CONFUSION BTWN DEP; TWR; PLT AS TO EXACTLY HOW HIGH TO CLB. 2) THE DEP PLATES ARE AMBIGUOUS! IT APPEARS ON CANAL #3 (INCORRECTLY) THAT DME EQUIPPED ACFT MAY BE CLRED UP TO 2000 OR 3000' AND THAT NON DME EQUIPPED ACFT ON THE RIGHT SIDE OF THE PAGE MUST ADHERE TO WBOUND AND SBND AND WBOUND ALT RESTRICTIONS. SINCE WE WERE DME EQUIPPED I ASSUMED WE WERE TO CLB TO 3000' AS PER INSTRUCTIONS. PLEASE HELP STANDARDIZE THE CLB PROCS AT MIDWAY NO MATTER WHAT RWY YOU TKOF ON!!!