Nav Work 104 - Let's Talk Maps!

[Lurch]

Nav Work 104 - Let's talk maps!

Apparently I'm ambitious enough to do 2 in a month.

Other Nav Threads:
Nav Work 101 - Cardinal Directions and Declination
Nav Work 102 - Crazy Magnets and Stuff
Nav Work 103 - Pacing, Obstacles, and Nav-Nerds

There is a LOT we could talk about when it comes to map. So I'm going to cut a few things out. I'm not going to discuss the multitude of options out there when it comes to web based interfaces and free mapping options. USGS, and a number of other sources all have digital versions of full quads available for free, and there are countless options for and a ton of threads already out there with alternate models.

I'm going to stick to the "normal" USGS 7.5' Quadrangles for this talk, we can get into other's later if people are truly interested in that.

7.5' Quads

So first off, lets be clear about what we're talking about here. For many decades, the USGS quad's have been the go-to map for wilderness folk, be it hunters or hikers. There are many other options out there, but most of those are using data pulled from these original maps. There is a TON of information on these maps, that most people ignore completely. I'm going to touch on a small fraction of it.

These are referred to as "7 1/2 minute quadrangles". When we get into Latitude and Longitude later this will make more sense, but the basics is that Lat/Long can be written in Degrees, Minutes, Seconds. Where 60 minutes of angle = 1 degree. These maps cover 7.5 Minutes of latitude and longitude. This is why maps down south are more square in comparison to ours up here... but that's a different talk to be had. The 'quadrangle' bit is simply a rectangle, or square like shape..

If you pack this full map into the field with you, you're a crazy person. But I've seen it done before so we'll chat about it

The Legend

The Legend of the map is basically anything around the boarder that isn't actually part of the map. Starting down in the lower left corner, you'll see something like this:

This little paragraph gives you a ton of information, the important bits for this particular map are that they did revisions based on aerial photography in 1993, and a partial field check completed in 1994. Any thing that was done *since* then will not be represented accurately. In the last 20 years roads may have been moved, closed, or rebuilt. Additional trails could have been created, and a whole host of other things. It also describes the different markings for the primary map datum in NAD27, and the datum shift for NAD83 is marked in the corner.

I'll talk more about map datum's in a future thread when we get into the various coordinate systems, but for now all you need to know is that it's important when want to describe coordinates, but *not* important in relation to bearings and the like.

Now we're into the center of the legend. Working our way from left to right, top to bottom I'll go over the various bits in here.

• North Reference: This is really 3 arrows in one
  • True North: This would be the one designate with a *, by default would normally be the *top* of the map, and the both sides of the map should also be referenced in true
  • Grid North: Designated by a GN, this is the coordinate grid as it's overlayed onto the map, and it's relation to True while using UTM. Because we're fairly close to the central meridian in this case it's only 0° 40' E of true. For all intents and purposes this is below our margin of error, and I generally treat True and Grid to be interchangeable. That is NOT always the case, and will depend on the map, and its location. So please at least be aware of the difference
  • Magnetic North: MN is going to be accurate to the date listed. As we've discussed before MN is moving, and is currently just a smidge under 15°E for this area. In 1995 when this map was made it was 18.5°E
• Ratio Scale: A normal 7.5' quad is going to be printed at 1:24,000. This is a direct ratio, so 1 inch on the map, would equal 24,000 inches (2,000 feet) on the ground. Regardless of what this number *says* if you are printing maps yourself, and your printer does any sort of scaling it probably won't truly accurate.
• Bar Scale: This is one you can actually use for measurements. So long as it is scaled the same as the rest of the map, it will remain accurate. I don't think I need to explain how to us the bar scales but if anyone is curious about it I can explain
• Contour Interval: I'll discuss contour lines below a little bit, but they are the visual representation to tell topography and elevation. The interval listed is describing how many vertical feet are between lines. Generally the contour interval is either going to be 40' or 20', although with newer maps, and the availability of DEM's this could be customized, so don't take that for granted. (Note: this will also tell you what vertical datum the map is using)
• Quadrangle Location:This is going to show where the map is within the state. The small black dot on there is the coverage of this particular map.
• Adjoining Quads: This 'tic tac toe' grid is listing out the names for the maps that are surrounding this one

Down in the lower right is going to be some additional information. Depending on the type of map, print series and a number of other things you may have a very limited 'symbol' key. The important bit in this section though is that it's giving you the name of the map. Multnomah Falls, Oreg - Wash. The name itself is given after what's considered the "most prominent" either cultural or geographical landmark. That may have changed since the creation of the original map for that are, which is why you'll sometimes have maps named after something that doesn't even appear on the map. If it's titled after a major railroad depot that is no longer in existence, or a landmark that has subsequently been flooded by a dam, it can be a little odd. In addition to that it gives the index name for this particular map, which in itself has a wealth of information. 45122-E1-TF-024 Lets break that down to learn a few things.

45122 saying this map falls into 45°N 122°W. We need to be a little more accurate than that though, since this is only 7.5' (minute) map, and there are 60 minutes in a Degree, that entire 45°N 122°W is covered by an 8x8 set of 64 possible maps.

E1 is the 'area reference' code for that 8x8 grid of maps covering the area. This grid is numbered sequentially left to right (East -> West) from 1-8 (remember we're counting Degrees West here, so numbers go up as they go West) and A-H from South -> North. This map is E1 so in the larger view of 45122 we're a little north of center, and on the eastern edge.

TF = Topographic Map, with contour values in Feet

024 = 1:24,000 Scale

The Map

Remember this image, we'll be talking about it more!

The whole point of these maps is to be able to read the topography of the ground, make sense of land features and tie it all together. There are a number of map symbols just in the small chunk shown above, but we'll go through this one piece at a time, starting with contour lines.

There are two main types of contour lines, intermediate, and index. The index contours are the darker brown lines, that will usually have a number written on them. These lines represent an elevation, and every point along that line will be that elevation. Between Index contours there will be 4 intermediate ones. If you're unsure of the contour interval, it's just some simple math to find two adjacent Index lines, and divide their difference by 5. In this case we can plainly see the 3400' line, 5 lines up from that is the 3600' line. That's a 200' difference, divided by 5 lines means each line represents an elevation change of 40 feet.

You can think of this as layers on a cake, which each line just being a horizontal slice

contours.jpg (13.59 KiB) Viewed 4792 times

By studying these, you'll learn to identify land features and essentially build up a little model in your head to help tie reality to the map. To make this a little more visual and help people understand that relationship from a flat map to 3 dimensions I *made* my own model a few years ago.

This is Postage Stamp Butte for anyone that wants to look it up. Obviously seeing it in person is far more helpful than looking at a picture of a 3D model built off a 2D representation of a real land feature, but it's a helpful model to make sense of how different shapes of the contour line will relate back to the real world

There are a few important things to remember when it comes to contours though, and to help you rationalize and problem solve things for yourself.

1. Contour lines always form closed loops. These may not close within the confines of your map, but they *will* close at some point. A contour line will not just dead end, and it will not cross another one. There are rare exceptions where the cliff is too steep and tall for the map makers to simply draw all those lines in, but that's rare, and should be obvious.
2. The closer together the contour lines the steeper the terrain. Further apart = flatter.
3. Be careful, since adjoining maps may have different contour intervals. If you're looking at a map with a 40' and a 20' interval, the 20' contour interval will look steep and scary as hell. If something isn't looking right, take a second to think about it deeper.
4. Both a ridge line, and a valley can form a V type shape in the contour lines. There is a trick to determine which is which though!
   • Ridgeline: First rule, creeks don't flow on ridges! Secondly ridges tend to be more rounded. If you can Identify the V or U shape that the contour lines are making the point of the V will be pointing DOWNHILL.
   • Valley: Creeks DO flow in valleys. The point of the V formed by these contours will be pointing to the UPHILL side.
5. Always pay attention to which way is up! One of my favorite questions is to give someone a small piece of a map and ask them to identify the highest and lowest spots. First one to tell me what the highest and lowest point of the topo map I posted above is wins a virtual cookie!

Symbols & Colors

There are a TON of map symbols that USGS uses. You can check out a good PDF of them over HERE

Color wise you can think of things generally along these lines.

BLACK is usually manmade things that actually exist. Obvious exceptions for borders, like county lines, reservations etc. In the above map those roads, powerlines, and trails are physical things that are actually there.
GREEN is simply vegetation, or forester area
RED is mostly informational. The red numbers in boxes are showing road numbers. The dashed red line and large 26 is part of the Township & Range "coordinate system", and while there are *some* things that are actually out there, the majority of red things on the map don't acutally exist.
BLUE obviously represents water
WHITE contrary to popular belief is not snow, but simply a lack of vegetation. Most of the white splotches that you see scattered throughout the maps in the gorge are showing skree fields or rock falls where there is no significant vegetation. In the map above, the white slash that follows the powerlines is showing the lack of trees under/around those powerlines.
PURPLE You'll see some bright purple on some maps, generally this is provisional information, or expected development that was planned for, but not actually in existance when the map was last revised. You'll see a lot of this around Portland
BROWN is typically reserved for terrain, contour lines and the like. If you have an old "Provisional" map, than a lot of the "black" will actually be printed in brown, including the entire legend.

I'll let you go through the symbols in in the PDF above, and if there are any questions out there on anything I'm more than happy to discuss it, it's just too much material to really go over it all in here.

Map & Compass

Just a disclaimer going into this section (and all these threads really), there are multiple ways to do all of these techniques, I'm simply sharing the ones that I primarily teach, and have found to be the best for the balance of simplicity and accuracy. I'm not saying that other methods are wrong, I'm just giving you one way to do it.

Orienting a Map
This process is simply to make North on the map, be North in the real world. It's not absolutely necessary, especially if you've got a good enough mental map going. But it can be helpful to orient yourself, and make the landmarks in front of you be a bit more relative to what you're seeing on the map.

The first thing you're going to do is set your compass to 0°T (or 360°) like you're shooting a bearing due North (assuming that your compass is properly declinated). Note the black 'Orienteering Lines' that are always running N/S under the needle inside the compass.

Next you have a couple options. You're going to want to line the compass up so that those orienteering lines are parallel to a reliable N/S reference on the map. You have a couple options to work from on *most* maps.

• UTM Grid: This is the grid used in establishing UTM coordinates for locations. A lot of maps will have this grid drawn across it, but not all. These will be oriented to GRID north. For our region since its less than 1° off I would call it good enough.
• Township & Range Lines: This is more of a last resort. Just looking at the map you can tell that they aren't all that accurate, but in a pinch they'll work as a good guesstimation.
• The Edge of the Map: Any topo worth its salt, as long as it hasn't been cut down by someone else will have the borders be aligned to TRUE north.

You can either line the edge of the compass up with one of these lines, or the orienteering lines. In this case since we're shooting 0° they're all the same. Make sure North on the compass is North on the map, you don't want to do this backwards!

You're then going to rotate the map and compass all together, until you put Red in the Shed.

This is the only common map and compass skill where you will be using the needle in the compass. This is hugely important and most people get screwed up with bearings because they're trying to include the needle in some fashion, so I cannot stress that enough. For the rest of this post you will NOT be using the needle in your compass for finding or plotting bearings on the map, your compass has essentially become the most expensive protractor you've ever purchased!

Finding a Bearing

We're going to find the bearing from Sherrard Point, to the trail junction of 444 and 424. First we're going to draw the line that we want to shoot. Then first lets do a common sense assessment here. We know our compass rose

North = 0
East = 90
South = 180
West = 270

Just by looking at this bearing we can tell it's going ENE. (East North East) so we know it HAS to be between 0-90. NorthEast would be at 45, and since it's more east than that we can further narrow it down that it MUST be between 45-90°T (closer to 90)

Lay your compass down so that the edge of the compass is right on your bearing. Have the mirror in the direction of travel. We want the bearing from Sherrard, TO the trail, not from the trail to Sherrard in this case.

You're then going to rotate the Bezel of the compass, until the orienteering lines are lined up with one of those quality N/S references we talked about before. Make sure you're putting North, North! You can slide the compass along that bearing as needed to make sure you have an accurate reference just make sure the edge is lined up as accurately as possible.

Once your orienteering lines are parallel, you can read the bearing from the 'direction of travel' mark up by the mirror. In this case it looks to be about 81°T, which would fit into our earlier assessment as East North East, and between 45 and 90° (Closer to 90)

Plotting a Bearing

Now we need to know how to shoot a bearing, and plot it onto the map. Say we want to draw a line at 290°T from Sherrard. Maybe I'm standing at a known location, and my GPS is giving me a GoTo bearing that I want to plot onto my map. Or your following a treasure map, or who knows why you need to, but it's the other half of the skill so we'll talk about it here

First things first, set your bezel to 290°

We'll do the same common sense assessment, and we know that 290 is between 270 (west) and 360 (north). Far closer to West actually, so this bearing should be going West North West. If you draw it out and it's NOT doing that, I like to call that a clue, and you need to pause and reassess what you've done.

Place the edge of your compass on the point that you're drawing from.

Since our bezel is set to the desired bearing that is not going to move, we're going to use the edge of the compass, and our point of origin as our pivot point, and rotate the entire compass around that point until we have our orienteering lines lined up, double check that North is North, and triple check that our bearing is indeed following our earlier assessment.

Then it's simply a matter of drawing the line, and we're done! Success! Bearing plotted, and it is indeed running roughly WNW

I have apparently overfilled my attachment abilities for this thread, so we're going to end it here! I've got a few more things we can go over for map and compass, and some coordinate system goodies too.

Until next time!

[kepPNW]

Don't think I've taken the chance to say this is just an incredibly rich set of postings, you're doing here! They should all be sticky'd, IMO. Thanks so much for them!

True North: This would be the one designate with a *, by default would normally be the *top* of the map, and the both sides of the map should also be referenced in true

Does that mean the sides converge, just as lines of longitude? I never realized that before, but it'd help explain the issues I've had stitching them together in the past.

Always pay attention to which way is up! One of my favorite questions is to give someone a small piece of a map and ask them to identify the highest and lowest spots. First one to tell me what the highest and lowest point of the topo map I posted above is wins a virtual cookie!

Mmmmmm, coooookie...

Spoiler: show

[Don Nelsen]

I really enjoy these map posts of your Lurch. Keep them coming! Oh, and the max el. on the map is >3840' but less than 3,880'. If I were to guess I'd say about 3,842 or 43. Min. is 2,000 or a fraction less since the lower right corner just touches the 2,000' contour and as near as I can see maybe just a bit under.

[Lurch]

kepPNW: Unfortunately you're a bit off on the low point There is a creek down in that corner, so the slope that your arrow is going to is actually going *up* on the far side of the creek.

Don: I believe that tiny loop of the index contour down on that corner would be the 2,200' line, not the 2,000.

I guess you both get half the cookie

[kepPNW]

kepPNW: Unfortunately you're a bit off on the low point There is a creek down in that corner, so the slope that your arrow is going to is actually going *up* on the far side of the creek.

Don: I believe that tiny loop of the index contour down on that corner would be the 2,200' line, not the 2,000.

I guess you both get half the cookie

D'oh! I didn't even spot the creek initially, but now that you point it out it's totally obvious. I guess that line looked more black than blue on the posted map. Y'know, I was looking for a trick, too. I saw a little spot on the hilltop, but I think that's just an image artifact. (It's not on the downloadable PDF! Yes, I looked. ) Half a cookie's still good, though. Heheh...

Corrected

[Lurch]

Huh, didn't notice that speck, I didn't put it there either though so not sure where it came from.

You're new line is on the uphill side of the creek though Remember that valleys are cut into the hills, and the V points uphill Don't make me take my cookie back!

[kepPNW]

You're new line is on the uphill side of the creek though Remember that valleys are cut into the hills, and the V points uphill Don't make me take my cookie back!

Argh! Umm, the other arrow obscured the whole mess...

[Eric Peterson]

I love me sum maps!!

Nice set of tutorials so far Lurch!

[Don Nelsen]

I believe that tiny loop of the index contour down on that corner would be the 2,200' line, not the 2,000.

I guess you both get half the cookie

Yes, now I see - you are right. That'll teach me to try to look at things on my I-phone!

dn

[texasbb]

Thanks, Lurch, for posting this (and the previous ones). Very good info, very well written! I found myself teaching this kind of thing for the first time this year and these write-ups would have been very good reference material. They're links I'll keep bookmarked and give to others as well.

I have one question/comment. You explain how to orient the map, then do all your bearings work from that framework. I've personally found that approach to be difficult to use in practice. I can almost never find a flat, dry surface when I need one, and when I can, the wind often makes it practically imposible to keep things aligned. And sometimes the flat surface even interferes with the compass needle (nails/screws in a table top, iron ore in the ground, etc.). I usually end up doing map bearings with a half folded, half wadded map pressed against my thigh or something, then convert to magnetic bearings for travel. So that's how I taught it--keep map and magnetic work separate. A couple of folks in the class who'd done some map work didn't like my approach. Thoughts?