Distances are measured using a grid system matched to each ballpark's unique parameters and configuration. If every team worked according to the MCI plan, each stadium would be accurately diagramed with a fine-grained grid related to its seating sections, level by level. This would tell the estimator how far the ball was from home plate when it landed in the seats, bullpen, or other stadium area, and how high it was above field level when it landed. Click here for the formula. Some teams work from arcs rather than grids, making the estimators' jobs more difficult.
Some teams measure only to the point of impact, rather than to the likely field-level landing point.
The Rockies don't have height data, and must estimate that dimension. Baseball, a game of inches and meticulous record-keeping, deserves accurate and consistent data, and these awful numbers have already tainted one set of record books. Click here for the story. Now is the time for scientists to review and refine the system and for Major League Baseball to ensure compliance and train the estimators. After a period of adjustment, during which many long home runs will seem puny, we'll slowly reacclimate ourselves to reality.