Area: Estimating and Calculate the Area of Rectangles . Area is a measurement of 2D space. Because there are two dimensions, the units for measuring area need to also be 2D shapes. Rectangles fit together without gaps or overlaps and will fill or cover the area of larger rectangles exactly when arranged in rows and columns. . Arrays are arrangements of rectangles in rows and columns. The number of rows in an array can be multiplied by the number of columns to find how many small rectangles are i