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?