How Do You Figure Out Coordinates?

How to Figure Out Coordinates on a Construction Site

Why do we so often find ourselves begging for coordinates at the start of a project—when we all know we need them? It’s frustrating, inefficient, and unnecessary. This blog is here to help you cut through the chaos and get your site layout process locked in from the very beginning.

Whether you’re a field engineer, surveyor, or builder, the concept is the same: you need a solid basis of bearings and accurate building coordinates to do your job right. In this blog, I’ll walk you through the exact process our team followed on a multifamily project and show you a clear method for obtaining and confirming coordinates using verified data.

Step 1: Understand the Basis of Bearings:

Your basis of bearings is the starting point. The civil engineering team typically includes this in the drawings using northing, easting, and elevation references. However, it’s critical not to rely solely on CAD files. Instead, back up this data with an RFI or confirmation from city records. In our case, we combined the CAD data with aerial maps and the topographic survey to cross-verify coordinates before submitting our RFI.

Step 2: Confirm Building Locations:

Once we had the basis of bearings, we needed to locate the buildings. Again, relying only on CAD files is a no-go. Instead, we created an exhibit with two gridline intersections per building, verified those against the basis of bearings, and submitted an official RFI to confirm accuracy. The surveyor responded with a formal deliverable—a coordinate system with labeled gridline intersections. That documentation can now be inserted into the drawing set.

Step 3: Establish Primary and Secondary Control:

With verified coordinates, we could then establish primary control points around the site. Think of these as your permanent external reference. Using the compass rule and traverse methods, we connected these control points to the basis of bearings and property corners, creating a full primary control network.

Then, inside the site, we set up secondary control: baselines and gridlines for each building. This internal control allows us to precisely lay out walls, columns, and other structural elements using working control lines.

The Key Principle:

At the end of the day, here’s what matters:

• Your basis of bearings must match your building coordinates.
• That alignment allows you to build a reliable primary control network.
• From there, establish secondary control to manage layout within each building.
• Finally, use working control to install components precisely where they belong.

Final Thoughts:

As a builder, I always want:

1. Confirmed basis of bearings—verified through the city or official channels.
2. An official deliverable—either a drawing sheet or an RFI with exact building coordinates.

Don’t wait until layout to figure this out. Start early in pre-construction. Engage your surveyor. Equip your field engineers. And be prepared with the tools and training to do it right.