Green Valley Recreation Hiking Club
January/February 2020
First class◦ Marginal information
incl north(s), contour interval, legend (or key)
◦ Scale
◦ Grid reference
Second class◦ Contours and how they show terrain
◦ Route selection
Third class ◦ How to determine a bearing from a map
Magnetic declination and how to compensate
◦ Back bearings
Importance of map
and compass
Importance of map
and compass
NPS, REI include GPS
A map is a 2 dimensional representation of the 3 dimensional ground
A topographical map shows relief – the topography - of the land. There are several ways it does this.
Marginal information is that information available on maps around their borders
Varies depending on map maker, country
We will be using USGS maps or maps copied from USGS maps
Lots of useful information
Name of map, 7.5 series Lat and long at corners, ticks every 2.5’ UTM coordinates USGS Date Datum – NAD 27, NAD 83, WGS 84
North (GN, ⋆, MN)
Scale – 1:24,000 Contour interval Symbols Adjacent maps
True north◦ the north pole◦ direction represented by
meridians of longitude◦ map margins
Grid north◦ corresponds to vertical grid
lines◦ can be different systems
Magnetic north◦ points to magnetic north pole◦ the pole drifts◦ averaged for middle of map
Can set GPS for grid or mag Can set GPS for UTM grid or
lat and long or both
Magnetic declination 2010
Geophysical Data Center’s declination calc:
Mag declination 85614 on Jan 3 2020 9º35 ́ +/-21 ́Changes 6 ́W eer yr
1998: 11º 37.0 ́
Symbols on a map represent features on the ground
USGS use nearly 100 symbols on their topographical maps
Symbols are not universally standard – need legend or key
Symbols not to scale – usually larger
Use center of symbol
Find an example:
Intermittent stream
Cemetery
Spot elevation
Building
Shrubland
Tank
Unimproved road
Mine shaft
Mine tunnel/shaft
Ratio of a distance on the map to the corresponding distance on the ground
1:24,000 means that one inch (foot, cm, etc) represents 24,000 inches on the ground
A small scale map covers a large area; a large scale map covers a small area
We will be using meters
Mils (milliradian) = 6283.185/circle ~ 6200 - 6400 / circle
17.8 mils in a degree
One mil subtends one meter at 1000
Units
Kilometer 1,000 meters 0.62 miles
Mile 1,609 meters 1.6 kilometers
Meter 39.37 inches 1.09 yards
Scale One inch equals One centimeter equals
1:5,000 417 ft 50 m
1:10,000 833 ft 100 m
1:20,000 1,600 ft 200 m
1:24,000 2,000 ft 240 m
1:25,000 2,083 ft 250 m
1:50,000 4,167 ft (0.8 mi) 500 m
1:63,360 1 mi 634 m
Measuring distance
• Use scale, or• Grid lines = 1 km• Divided in 10ths
Use the edge of paper or string to measure distance
Then align it with the scale or edge of map
Grid lines are 1 km apart on 1:24,000 maps.
To convert km to mi:I km = 5/8 mi1 mi = 1.6 km
Practice
How far is it:
1. From the water tower (WT) to the water tank in McGeesSettlement in meters?
2. From the WT in McGees Settlement to Samaniego Peak as the crow flies?
3. From the cemetery to Sand Tank following the track?
Contour lines
•Show relief of the earth
•Each line represents a constant elevation above sea level
•Index lines are thicker and labeled with height
• Intermediate lines are between index lines
•Dotted lines are approx
The space between contour lines represent a constant vertical distance above sea level –the contour interval
Contour intervals are not constant between maps
Contour interval is noted on map – or can figure it out
22222
300
400
. 473
What is the contour interval on your map?
Contour interval = 40 ft
Index line
Intermediate line
Contour interval = 50 units
What is the contour interval?
There are many different systems that provide a numeric representation of a position on the earth:◦ Universal Transverse Mercator (UTM) – we will be using
UTM to give us a grid reference◦ Latitude/Longitude◦ State Plane◦ Many more
Why should you know how to find a UTM grid reference from a topo map?◦ Relate a location to someone else ◦ Map to GPS and back◦ Most useful GPS feature is to verify your loc on a map
To find the GR of the church:
1. Grid line to the west is 91
2. Number of 10ths east = 6, giving an easting of 916
3. Grid line to the south is 94
4. Number of 10ths north = 4, giving a northing of 944
5. Combine them to get a six figure GR of 916944
In the house, then up the stairs
Grid referenceTo find the UTM coordinate of Samaniego Peak:
1. Find the number of the grid line to the west – it is 81
2. Estimate the number of 10ths east of this line. This is 1, giving an easting of 811
3. Find the number of the grid line to the south – it is 30
4. Estimate the number of 10ths north of this line. This is 4, giving a northing of 304
5. Combine the easting and northing to get a six figure GR of 811304
Grid reference – practice
Eastings, then northings, or go east, then north --
Find the UTM coordinate of hill feature 5343 east of SamaniegoPeak?
What is the grid reference of the cemetery just west of McGeesSettlement?
Grid reference -expanding to full UTM
GR of cemetery: 828284
To talk to others and your GPS:
Expand to a 10 figure GR:8280028400
Add the first two digits of the eastings and northings:
0482800 E3528400 N
Add the zone (12):12 0482800 E
3528400 N
Location:
12 0482036 E 3529352 N
Center of map
60 zones of 6 degrees of longitude. 20 designations of 8 degrees of latitude. W e’re in 12 R
Grid reference
The cemetery is atGR 828 284
A 6 figure GR refers to a square 100 m X 100 m
An 8 figure GR refers to a square 10m X 10 m
A GPS gives a 10 figure GR
With a home made romerwe can get a reasonable 8 figure GR
To make a romer, use the side of the map
0686 4446
Grid reference
Go east, then north --“into the house and ue the stairs”
The cemetery is at GR 828 284
With a romer,
8 figure - GR 8280 284510 figure GR 82800 28450
How far is it from Samaniego Peak to the spot height at GR 823 304, in meters?
What is the vegetation at GR835 298?
What is the GR of Shloh Well (8 fig GR)?
What is at GR828 313?
What is at GR8281 3138?
The GPS says we are at 12 0481803 E 3527848 N. Where are we?
The GPS says we are at 12 0482581 E 3529296 N. Where are we?
Shloh Well is at 8169 2774. What would we enter into the GPS?
We are at GR828 313 (the woodland). What would we enter into the GPS?
We are at GR8281 3138 (end of trail)? What would we enter into the GPS?