US/Canada flag positions on Rainbow Bridge, Niagara Falls

Here we are at the International Boundary Line plaque, Oct. 11, 2022.

We turn around and... why aren't we looking directly halfway between the two nations' flags? Doesn't the boundary cut across the bridge at an 90° angle, perpendicular?

What angle does the boundary cross the bridge?

Hmmm, to get the boundary vs. bridge angle, we need the bridge vs. north, and boundary vs. north angles. I.e., their azimuths.

We determined the azimuth of the bridge from various aerial imagery. Note 1.

For the boundary data we went straight to the International Boundary Commission website. We then calculated, facing downstream, that the boundary proceeds 2.9° left of the perpendicular to the bridge.

What angles are the flags to the perpendicular, viewed from the plaque?

I. e., standing at the plaque and looking downstream perpendicular to the bridge, we expect to be looking directly between the two flags. Each of them should be at the same angle, one to the right, one to the left. But what angles are they actually?

We will get those angles from the aerial imagery. But wait! Where's the plaque? How are we going to be "standing at the plaque" if we can't find it on the aerial imagery?

It's a vertical feature directly below the railing. How are we going to see that on (vertical) aerial imagery?

In most aerial imagery one would need the sun coming from certain angles to make a shadow on the bridge, so we can tell where below the railing the plaque is affixed.

In steps the manhole cover

Note 2. Ah, but we are in luck: a lowly manhole cover comes to our rescue! We can't see the plaque on aerial imagery, but we can see the rectangular manhole cover at its feet. Photos:

Manhole cover / plaque relationship

So from the above photos we see the rectangular metal manhole plate on the surface of the sidewalk is 4/5ths in the USA, 1/5th in Canada. So we now know where the plaque is hiding under the railing. Ah ha.

Angles, from aerial imagery

So now that we know where the plaque should be on various aerial imagery, we measure using various graphics programs on our computer screen. For completeness we toss in the boundary angle calculated above:

Table 1: Angles from plaque perpendicular to bridge, and distances along the median strip. (Positive: right, negative: left.) Calculation 2. Approximate of course:

Object ° m
Canadian flag -30 -6.4
Street lamp -12 -2.3
Boundary -2.9 -0.6
Perpendicular 0 0
US flag 9 1.7

Yes, we calculate Canadian flag --> 4 m <-- street lamp --> 4 m <-- US flag.

White stripes going across the road

We also notice the three white lines on the pavement crossing the road. On aerial imagery we see the middle line extends the white line of the 1970's photos that chopped the 4/5ths of the manhole cover. Indeed, that middle line is our often mentioned perpendicular to the bridge from the plaque, and agrees with our above Table 1, expressed as a line along the median strip:

Canadian flag --> 4 m <-- street lamp --> 2.3 m <-- Perpendicular --> 1.7 m <-- US flag.

Including the invisible boundary:

Canadian flag --> 4 m <-- Street lamp --> 1.7 m <-- Boundary --> 0.6 m <-- Perpendicular --> 1.7 m <-- US flag.

It is a good thing the three lines seem only to be painted on the two to USA traffic lanes (upstream half of the bridge,) as by the time they hit the median strip the middle one is already 0.6 meters away from the actual boundary. Note 4.

But that's not as far as that street lamp, which most people would assume should be smack dab on the boundary, but instead is 2.3 meters off.

So what about that street lamp?

Observation: From aerial imagery we see the median strip has regularly spaced street lamps about every 36 meters. They were certainly there before the flags were moved, from the railing as seen in the 1970 photos, to the median strip.

I bet that the US and Canadian flags were simply placed symmetrically around the already existing street lamp. And that lamp was not especially placed upon the border in the first place, but instead just at its regular interval of all lamps on the bridge. All reasonable so far.

What would you do as an administrator?

If I were in charge, and somebody handed me an order "move the flags from the railing to the center strip," would I go

Or simply placing the flags in a pleasing symmetric fashion around the existing lighting... makes sense!:

Conclusion and recommendations

So what we're seeing is again (calculation 5, total length 8.1 meters):

C -------------------- L --------- B --- P -------- U

🇨🇦 -------------------- 💡 --------- 🎌 --- 👁 -------- 🇺🇸

So the border runs not halfway between the current US and Canadian flags, but instead rather closer to the US flag.

Perhaps a small supplemental ornamental boundary monument could be placed at the exact spot on the median strip. It would already be among the flagpoles and street lamp, so shouldn't affect traffic safety. Yes, a small version of the usual monument.

By the same author

US/Canada 49th Parallel boundary monument trip, 1994.


  1. Indeed, the reader should have their favorite aerial imagery, and Streetside, (no Street View on the bridge, oddly) on their computer screen to follow along with the rest of the story. (And to do their own armchair investigations of other international bridges (and tunnels!) perhaps.)

  2. "In steps the manhole cover", not "step in the manhole..." Ha ha.

    Imagine that, a "pedestrian" manhole cover being the "Rosetta Stone" allowing us to tie the two parts of our foray into forensic geographical nitpicking together! The Rosetta Manhole Cover.

  3. And as of 2022 (looking my family photos) I can confirm the manhole and plaque are still in the same spot.

    (In the above 1970's photos we see perhaps two additional plaques on the right. I didn't notice any on my 2022 trip.)

    We also notice the flags that have now been moved to the median strip, with a street lamp instead of the United Nations flag in the middle. (No conspiracy theories. As we will see, the street lamp was there first!)

  4. Is one sure one wants to paint odd lines on roads? Doesn't sound like it is consistent with the traffic rule book. How about instead a nice additional mini-monument on the median strip?

  5. The careful reader will note that all along we have put 100% confidence upon the position of the plaque. We, for instance, have not stepped back and in our geographic information systems drawn a line between TP 135 and 136 and seen how close that crosses through the plaque on aerial imagery (which of course has alignment debates itself.)

    Indeed, all we are saying is, "Odd. Standing at the plaque, why aren't I looking halfway between the two flags?"


  1. I also found an earlier (1913) definition of the coordinates of TP135 and TP136, but the azimuth between them was the same as the current azimuth.

Dan Jacobson

Last modified: 2022-11-28 07:48:57 UTC