doing a report for school !
Often, a plan is drawn in grid form. Each square of the grid is equal to 3', or something similar. That type of plan is much easier to work with, since the page is not covered with dimensions. If a particular feature, such as a wall, is not located on a grid line, there will be a dimension from the grid line to locate it. The suspension system for a dropped ceiling is also called the grid. Main runners are spaced every 4', then a system of tees is used to divide the ceiling into a grid of 2' x 2' or 2' x 4' spaces. Light fixtures and HVAC vents are made in sizes to fit in the grid. Hope this helps you with your project.
