Section 07: Map Reading

If you're interested in what tree planting is all about, or you've been offered a job as a planter, this forum will give you a great head start on learning the ropes.
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Section 07: Map Reading

Post by Scooter » Fri Feb 13, 2015 4:42 pm

In this section we'll learn a few basics about Map Reading. We'll also talk about how to understand map directions, coordinate systems, topography, contour lines, scales, and geo-referenced digital maps.


Upgraded video, released in 2017




All planters should have a basic understanding of maps and cartography. One of the benefits of becoming a tree planter is that you'll learn a lot about the world around you, including things like being able to tell directions without a compass.

Let's start with the very basics. On most maps, all the writing is oriented the same way, so you can determine a "top" and a "bottom" to the map. If the map doesn't indicate otherwise, the top of the map is always north. This is the case in probably 99% of maps. Occasionally, for some odd reason, north will face a different direction, but if it does, there should be a little compass rose symbol or arrow on the map that points to north.


GPS System

Most maps that planters use in British Columbia will also have coordinates on them. There are literally thousands of different coordinate systems in place throughout the world. Some of them were created centuries ago by early explorers and surveyors, and it's safe to say that most are extremely confusing. Within BC, you'll normally just encounter one of the most well-known systems used today, a traditional Latitude and Longitude system. The Latitude and Longitude coordinates will be in "northings" and "westings" when you refer to coordinates within British Columbia.

Northings, or the distance north of the equator, range from about 49 degrees at the bottom of BC to about 60 degrees at the top of the province. These are also known as the latitude. Westings range from approximately 114 to 140 degrees, with the lower numbers on the east side bordering Alberta. These are known as the longitude. If you have problems with respect to latitude and longitude in terms of remembering which is which, think of the word "flatitude" instead of latitude. Latitude lines are flat lines, rather than vertical, when you look at a map. If you're ever using software or a GIS system that doesn't allow you to type in the letters N or W to represent northing and westing, use positive numbers for the northings, and use a negative sign for the westings. The number representing the latitude always comes first, before the number for the longitude.

If you get a block map, sometimes it will display the coordinates on the sides of the map, in a scale. As mentioned, the latitude is the distance above or below the equator, hence the reason why latitudes are always "north" in British Columbia. That's why the latitudes run up and down the sides of a map, even though a line of latitude is flat, running from left to right on a normal map. The longitude is the distance to the east or west of the Prime Meridian that runs north/south down through England, hence why longitudes are always "west" in British Columbia. That's why lines of longitude are vertical, and the longitude numbers always run along the bottom or top of a map.

In addition to the possibility of seeing latitudes and longitudes listed on the sides of your map, there may be a single point coordinate (latitude and longitude) listed somewhere in the map's key. That is probably for a point in the very center of the map, although occasionally, it will refer to a random point somewhere on the map where a surveyor decided to pick what's known as a "tie point" to start plots or something similar.

The Global Positioning Satellite system, also known as GPS, is a network of approximately thirty satellites that are operated by the US government. If you're at any point on Earth with a GPS device that can "see" three satellites, you'll be able to determine your exact position in terms of latitude and longitude. Add a fourth satellite, and you should also be able to get your elevation above sea level. That's a simplification, but good enough for our purposes.

The GPS system (also known as NAVSTAR) is the American variety of GNSS, or Global Navigation Satellite System. Russia has a GNSS called GLONASS. Other political entities (Japan, China, India, and the EU) are also in the process of deploying their own GNSS systems.

GPS coordinates are typically listed in degrees, minutes, and seconds. These refer to units of arc, or distance on the surface of the Earth. An arc-degree covers a very large amount of distance. The exact distance depends on where you're located on Earth, but an arc-degree can sometimes be as large as 65 kilometers or more. An arc-minute is smaller, maybe around a kilometer wide depending on your location. An arc-second is a pretty narrow range, only maybe around twenty to thirty meters wide, although again, this distance depends on your exact location. There are sixty arc-seconds in an arc-minute, and sixty arc-minutes in an arc-degree, just like in time-keeping. There are 360 arc-degrees to cover the entire surface of the Earth, just like there are 360 degrees in a circle. A lot of the time, people drop the "arc" prefix when they're talking about GPS coordinates, and just use the terms degrees, minutes, and seconds.

Sometimes, the written format of a GPS coordinate is written using specific symbols for degrees, minutes, and seconds. Degrees are symbolized by a small superscripted circle. Minutes are symbolized by an apostrophe. Seconds are symbolized by a quotation mark symbol. So for example, 54 degrees, 36 minutes, and 30 seconds would be listed as 54o 36' 30". At other times, decimal points will be used for either just the seconds, or sometimes for the minutes and seconds. In this example, if just the seconds were converted to decimal, the reading would be 54o 36.5'. That's because thirty seconds is 0.5 (or 30/60) of a minute. If the minutes were also converted to decimal, the reading would be 54.65o. That's because 36 minutes is 0.6 (or 36/60) of a degree. If you have a GPS device, you can go into the settings and pick the display format that you want to use.


Other Map Features

Your map may have a lot of curvy lines drawn all over it. These are called Contour lines. This means that the map is a topographic map, or one that identifies the topography of the area being mapped. The best part about a contour map or topo map is that it lets you understand the hills and valleys on a block, because the contour lines indicate the elevations throughout the block. Each contour line represents a specific elevation, say perhaps 1380m. Contour lines are usually spaced 10m or 20m apart on a block map, or perhaps 20m to 100m apart on a larger regional map. The closer the lines are together, the steeper the slope.

If your map doesn't have contour lines, but it has streams or creeks identified, there's a good chance that you can figure out a rough idea of the hills and valleys on your own. Streams and creeks are usually identified in blue. Look for a blue line, and follow that line to where it ends. If the line just stops suddenly, that's the highest part of the stream. Water flows downhill, so follow the creek away from the starting point where the stream officially begins, and you'll see where the block gets lower and lower in elevation. Perhaps the stream or creek will end in a blue pond, or join another larger stream.

Sometimes you can also guess approximate elevations on a map just by looking at the roads. The reason for this is because in hilly country, the odds are slightly higher that the roads on the block will generally be going uphill rather than downhill. Of course, it is possible that roads can go downhill upon entering a block, but that probably happens less than one third of the time, whereas more than two thirds of the time the roads are either flat or go uphill. The reason for this is simple. Logging companies like to harvest the easiest wood first, closest to the towns and mills. The easier wood near the valley bottoms was probably harvested years ago, and the logging companies are now making their way further and further up into the steeper ground. Also, it's easiest to build main roads along the valley bottoms and have then branches going up into the blocks in the hills. This method certainly isn't foolproof, but if you have to guess, you can sometimes increase your odds of guessing correctly to be slightly better than just 50/50.


Understanding Scales

Most maps have a small "scale" on them. This will be a number expressed as a ratio. On a map showing a small area such as a single block, the ratio is often 1:5,000 or 1:10,000 or, for a very large block, maybe 1:20,000. On a larger "area map" which shows a larger region of many blocks, the scale might be 1:30,000 or even 1:100,000 or larger.

This scale is a multiplier to indicate how much real distance is covered by each part of the map. You multiply the distance on the map by the large number in the ratio, to find the real-world distance. Usually, we think in terms of centimeters on the map. Therefore, if you were to have a map with a ratio of 1:5,000 then one centimeter on the map represents 5,000 centimeters in the real world. Ten centimeters on the map would be ten times that amount, or 50,000 centimeters in the bush. Now obviously, trying to measure real-world distances in centimeters is an exercise in futility. So you can convert those numbers to meters simply by dividing by 100, since there are 100cm in a meter. In other words, in the example where 1cm gave us 5,000 centimeters, that's equivalent to 50 meters. In the second example of 10 centimeters on the map, that becomes 50,000 centimeters or 500 meters in the bush.

These scales are really useful because they can help a planter or a foreman plan for how many trees need to go into an area. Let's say that you're looking at a map with your foreman, and you've identified exactly where your cache is located on the road on the map. Let's also say that you're looking at filling a big pocket. You can get a ruler out and measure from your cache to the back of the pocket. Let's assume in this case that it's 4 centimeters on the map from your cache to the back of your pocket, and let's assume that the scale on the map is 1:10,000. This means that the 4 centimeters on the map represents 400m in real-world distance. Let's also assume that your average spacing on this block needs to be 2.5m between trees. To go 400m to the back of your pocket, you need to bag up with 160 trees. You get this number by taking the distance (400m) and dividing your average spacing between trees (2.5m). But you'll also want to be able to plant back to your cache, instead of dead-walking, so you should take a minimum of about 320 trees in order to plant into the back, and then work back to your cache. If you can carry even more than 320 trees in your bags, that's even better, because you can plant the extras at the back before you turn around and plant back to your cache.


Geo-Referenced Digital Maps

One of the biggest revolutions in the planting industry since the introduction of LFH planting in the mid-1990's has been the introduction of digital maps, and in particular, geo-referencing.

When a digital map is geo-referenced, this means that it has actual GPS location metadata embedded within the file. Certain apps can load these maps into your mobile device and correlate the map with the actual current location of your mobile device, based on the GPS receiver in the device. If the app determines that you're actually "on" the map, it will display your exact location on the map with a little marker indicating where you're located, perhaps a blue dot or something similar. As you move around the block with your mobile device, your location indicator moves around on the map. It's just like using Google Maps or other similar services, except that these geo-referenced PDF's are generated by your silviculture forester and can show your planting blocks in great detail. Naturally, Google Maps focuses on towns and cities and government-maintained roads, so it usually isn't any good on remote planting blocks. At the moment, an app called Avenza PDF Maps seems to be the most popular way to work with geo-referenced maps.

Another bonus of apps that use geo-referenced maps is that you can do the same sort of distance calculations as what I explained in the example with the ruler a few minutes ago. You just tap two spots on the map (presumably your cache and the back of your piece) and the app tells you the exact distance between the two points. You can also outline an area, such as your entire piece, and the app will do an area calculation for you. Let's say that your area calculation shows that your piece is approximately 1.2Ha in size. If you're aiming for 2000 stems/Ha and you do a good job with your density, you can assume that your 1.2Ha piece should hold approximately 2400 trees. Being able to make calculations like this really helps with planning.


Always Know Where You Are

Understanding maps and coordinate systems can be far more confusing than what I've explained here, because the topic can be incredibly complex. However, if you master the basics that I've explained here, you'll understand all that you need to know to be comfortable with looking at a map and trying to figure out where you are. It's important that your foreman should always leave a map on the dashboard of the truck, so if there's an emergency and the foreman is incapacitated, the crew will be able to figure out exactly where they are and relay that information to outside help. If there isn’t such a map on the dash, ask your foreman to leave one there for emergencies, with appropriate contact information to reach outside help. If the foreman is the person who’s seriously hurt, he or she will be really glad that they left this information for the planters. Most companies require that each crew have a written Emergency Response Plan with all of this information, and with instructions on what to do in an emergency.

As a planter, you should always know the number of the block that you're working on. A great idea is for the foreman to use a dry-erase marker to write the block number on the rear-view mirror of each truck every morning. You should also be able to find the block number on the map on the dashboard.


Here's an audio version of this section of the tutorial series:


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