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8 Answers

What are the bolded obstacle heights for?

Asked by: 2894 views General Aviation

In the VFR sectional charts, some of the MSL heights for obstacles are written in bold. For example, here is a quadrangle from the Jacksonville sectional. I have drawn a red box around two heights which are bolded. What does the bold mean?

 

 

Jacksonville Quadrangle with Bolded Heights

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8 Answers



  1. Bryan on Feb 03, 2022

    I’m pretty sure that you have encountered printing artifacts. I do see what you’re talking about…you boxed the two and then there are the 444 top center, 390 on the right, and 419 in the lower right.

    The Aeronautical Chart User’s Guide (https://aeronav.faa.gov/user_guide/20220127/cug-complete.pdf) is the bible for how to read the charts. Page 12 has the information about man-made obstacles and it says nothing about different type faces. If there were a purpose behind it, this is where you would find the explanation. The fact that there is no mention of it is the reason I think it’s a printing artifact.

    Good eye.

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  2. natekfl on Feb 03, 2022

    In response to Bryan:

    Thanks for replying. I just find it very odd that these bolded heights are present in the source material (the pdfs/TIFFS at https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/vfr/), on pretty much every sectional, seemingly at random (or at least we can’t tell what purpose it serves). Given that it’s not in the Aeronautical Chart User’s Guide does lend to it being a mistake, I just find it really bizzare that they’re everywhere, it’s not like a one-off error.

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  3. John D Collins on Feb 04, 2022

    If you can’t find what you are looking for in a legend, you can download the entire current charting specification at https://www.faa.gov/air_traffic/flight_info/aeronav/iac/

    The IAC 2 is the specification for Sectionals.

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  4. Mark Kolber on Feb 04, 2022

    Yes, John, but there is nothing the the Sectional spec for bolded obstruction elevations.

    As natekfl points out, they are everywhere and there doesn’t appear to be a rhyme or reason to their use. At one time I thought it was based on some other feature which would hide unbolded text but there are a bunch of obstructions along that same railroad track far more hidden than the one in bold.

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  5. Russ Roslewski on Feb 04, 2022

    I don’t know all the ins and outs of the actual making-the-chart world. But I do know that it hasn’t actually been very long since chart-making was a very analog, manual process. Seriously, it only went all-digital in about the last 10 years or so.

    So I think what we’re seeing is pretty simple. Have you ever had a scanned-in document and tried to make some edit in Adobe Acrobat, and tried to get the font to match exactly? You twiddle around with font, bold vs. normal, font size and all the different options and you get something that’s pretty close, but still isn’t quite right? I’m pretty sure that’s what happened here.

    If you look closely, it’s not just the bold vs unbold. The AGL altitudes (those in parentheses) look slightly different too. Compare the 209 that’s in the red box with the 260 just to the right of it. They’re close, but not quite the same font type and size.

    My guess is that the bold ones are simply older, and the non-bold ones are the closest match using the current software. I say this because the non-bold ones “look” like a more modern font.

    However, I also want to know how you managed to post a picture on this forum. Can we do it in replies?

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  6. Mark Kolber on Feb 04, 2022

    Russ, I’ll try.

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  7. Mark Kolber on Feb 04, 2022

    Nope,

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  8. KDS on Feb 04, 2022

    I remember reading about “The cartographer’s art”. It was a discussion on why items on a chart do not exactly represent what is on the ground, but rather how showing what is on the ground is best illustrated. I remember the point being made that if it were not for that, maps would look more like photographs. Perhaps the answer lies in the cartographer’s judgment of how to best represent something.

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