Your parade unit id generally determines the location of your space in the lineup area. However, since different types of groups line up in different areas and are staggered into their final position at the lineup point, your unit number is not an indication of your exact position in the procession.
Unit numbers will be announced along with lineup instructions approximately 7 to 10 days prior to the parade. However, these numbers are prone to fluctuate as last-minute changes become necessary, so once the lineup is posted, check it often to be sure your lineup area hasn’t changed.