Land Nav Flashcards
What are the types of maps?
Planimetric
Topographic
Large scale USGS (United States Geological Survey)
Small scale Forest Service
What does a Planimetric map show?
Flat, no terrain shape information.
Typically show arrangement of features such as roads, buildings, water, fences, vegetation, bridges, railroads.
What does a Topographic map show?
Shows the Shape of the land.
Shows both natural and manmade features including mountains, valleys, plains, lakes, rivers, and vegetation, roads, boundaries, transmission lines, and major buildings and shows elevation with contour lines.
What does a large scale USGS map show?
Similar to a topo map with terrain detail but larger scales cover a smaller area in more detail.
What does a small scale Forest Service map show?
Smaller scale means it covers a larger area are the cost of less details.
What map scale is the Forest Service?
1:126,720
What map scale is Nat. Geo Map?
1:70,000
What scale is a 7.5 minute Topo map?
1:24,000
Why does distortion occur on a map?
Maps represent a curved surface on a flat piece of paper. Navigation usually takes place in a small area, on large scale maps where distortion is minimal and controllable
Projection is..
A method to put earth’s surface on flat map
Mercator Projection is used for
Used for topo maps
Major distortions
Preserves angles
What is datum?
A mathematical model used to calculate the size and shape of the earth
Which datum is based off of a single point?
NAD 27 (North American Datum of 1927). This is still used by forest services
NAD83 is based off of
250,000 points and 600 satellite Doppler stations
Which datum is used by the Global Positioning System?
World Geodetic System of 1984 (WGS 84)
Which datums are basically the same,and the most common on maps and used by Sheriff, D.P.S., CAP Rescue Aircraft etc?
NAD83 and WGS84
What is scale?
Ratio of map distance to ground distance in similar units
1:24,000 means..
1 inch on map = 24,000 inches on the ground.
1:250,000 covers a very large area
Graphic Mileage Scale- Map distance and ground distance are in different..
Different units. 7.5 min TOPO Map: 1 inch = 2,000 ft
Contour lines are commonly spaced..
20ft or 40ft (20 is more detailed)
Intermediate Contour- Thin lines, elevation not shown
Index Contour- Thick lines with elevation shown
What does a benchmark show?
elevation associated with ground marker i.e brass cap on ground
What is spot elevation on a map?
Elevation shown randomly, not associated with a marker
Forest Service map tidbits
½” = 1 mile
Range Lines- Run N and S
Township Lines- Run E and W
NO UTM coordinates
NO contour lines
USGS 7.5min Topo Map Tidbits
Large Scale, detailed view
Has much more information
Adjacent map names
Has UTM, Lat Long, and Range Township
UTM numbers around edge every 1000m**
Lat and Long marked on edge every 2.5 minutes**
NOT UPDATED OFTEN- features may not exist
Purple tint will indicate revisions from aerial photographs
Issues with map accuracy can include
Forest fires can create cleared areas which eventually become meadows
Meadows can fill in with trees
Roads are changed, closed, moved
Urban areas change frequently
Occasional publication/printing errors
Declination changes with time
Anatomy of a compass
Baseplate
Direction of travel arrow (does’t move, on baseplate)
Orienting arrow- align with needle during fieldwork
Magnetic needle- Aligns with earth’s magnetic field
Orienting lines- Align with North South on map
Index line- marks the bearing you set by rotating the compass housing
Cardinal Points on a compass
0 or 360*- N
90*- E
180*- S
270*- W
True north is
The axis around which the earth rotates
Magnetic north is
The direction your compass needle points
Declination is
Difference between true North and magnetic North
West USA (AZ)- has an EAST declination. I.E. magnetic North is GREATER than true North
East USA- has WEST declination so magnetic North is LESS than true North
Symbols and abbreviations regarding north
Star- True North
MN- Magnetic North
GN- Grid North
How do you use declination?
Magnetic to grid- Add declination “major to general= promotion”
Grid to magnetic- subtract declination “gen to maj= demotion”
Magnetic north is moving about 24 miles NW a year
Compass techniques: boxing the needle
Direction of travel arrow is placed where you want to go
Magnetic needle is placed in orienteering arrow
Compass techniques: establishing a bearing
Use dominant eye
Point direction of travel arrow in front of you to object
Box needle
Take reading and account for declination when transferring to map
Compass techniques: back bearing, or a reciprocal bearing
Direction of where you came
Same method as bearing but 180 degree difference
If original reading is less than 180, add 180
If original reading is greater than 180, subtract 180
“ I am 2 miles from High Mt. on a bearing of 250 degrees” When reporting, report the bearing FROM the reference feature
Compass techniques: measuring a map bearing
Line up compass on line between two objects
Put direction of travel arrow in the direction of travel
Line up N.S. orienting lines on the compass to N.S. lines on map
Ignore magnetic needle
This does not account for declination so keep that in mind
Compass techniques: intersection
The location of an unknown point by successively sighting it from at least two (preferably three) known positions
Your exact location must be known from each sighting
This is taking sightings of an object so that then you can go to a map and find out its exact location.
Compass techniques: resection
Determining your location by sighting two known positions
You must know your rough location and be able to see points on the map
Modified Resection
Only sighting one location and one linear feature that you are on, like a road
How to reduce error
A 1 degree error over 1 mile = approx. 100 ft. error. (greater distance sighted,the greater potential for error
Do short segments
Walking around an obstruction
Find an object on the bearing the other side and walk to it
Send someone around and have them line up to in bearing then walk to them
Count paces walking 90 degrees around it
Map and compass common errors
Using your compass as the Only Source of navigation information. Double check against the terrain and other info frequently
Not stopping when navigation info from map and compass and other sources doesn’t match up or seems marginal, stop and find the problem
Being pulled off your bearing by terrain such as slopes or something that interests you
Leaving your bearing to explore without a marker to get back on bearing
Not believing your compass when you get confused and lose confidence. Check it against someone else’s or against mapped terrain features.
Not knowing your exact starting point
Assuming you have an innate sense of direction and traveling with no map or compass
Letting navigation errors compound without correction
When working on map- having direction of travel or N.S. arrows backwards
Terrain features that can help orient you include
Safety Baseline
Major Feature
Obvious at night
Relatively close
Catch Feature
Feature on your route that you cross
Handrail
Feature along your route that you follow
Attack Point
Point to go to and then start micro navigation (bridge and road cross in the area)
Aiming off
Purposeful error to one side so you know which way to turn
Check point
Feature along route to check your location
Funneling
Features that funnel you to a point (ex. A stream and a ridgeline)
How do you find you pace count?
Walk 100 meters and count your number of paces
One pace is a left and right step
Average is your 100 meter pace count to use for pace beads
Account for weight of pack and slope when estimating how many steps it will take
Latitude and longitude formats.. what is used by DPS/dispatch?
Hemisphere degrees decimal minutes
This is also used by CAMRA, as well as UTM
Lat/long tidbits
Prime Meridian
0 degrees longitude
Equator
0 degrees latitude
Latitude
Degree distance is constant
Longitude
Degree distance is not constant (closer together near poles)
UTM (universal transverse mercator) tidbits
AZ in zones 11 and 12 (mostly 12)
Has Northing and Easting
7.5 min Topo, 1:24,000 scale
UTM Easting coordinates are measured relative to a central meridian (arbitrarily assigned at 500Km)
UTM Northing coordinates are measured relative to the equator
Incorporating GPS
CAMRA uses WGS84 datum
what is the current declination
Ranges from 10.33 degrees (yuma) to 8.65 degrees (apline). Phoenix is at 9.7 degrees
What 2 Datum’s are “essentially the same”
NAD83 and WGS84
