Grid line bubble
Labels one of the building's grid lines, the reference lines that locate columns and walls.
This explains what a symbol represents on a drawing. Conventions vary between firms and standards, and a drawing's own legend takes precedence.
How to read it
Under the A/E/C Graphics Standard the grid locates structural columns, load-bearing walls and shear walls, and is the basis for dimensioning. Vertical grid lines are numbered left to right at the top; horizontal ones are lettered bottom to top at the right, without the letters O and I, which could be read as 0 and 1. A column halfway between lines 2 and 3 is 2.5. Vermont's transportation agency uses the same grid bubbles to identify truss members on its bridge drawings.
Also searched as: column grid, grid marker.
More blueprint symbols
Sources
- A/E/C Graphics Standard, Release 2.2, ERDC/ITL SR-23-1, U.S. Army Engineer Research and Development Center, CAD/BIM Technology Center, sec. 3.3.1
- CADD Drafting Standards Manual, Section 7, Vermont Agency of Transportation, sec. 2.7
Last reviewed September 24, 2026 by Rory Hansen. How we research