FOR 375 Introduction to Spatial Analysis for Natural Resource Management – UPDATED 12.11.2015
Measurement Systems and Conversions
LENGTH
English
1 chain (ch)
10 chains
1 mile (mi)
= 66 feet (ft)
= 20 yards (yd)
= 1,760 yards = 80 chains
Metric
1 nanometer (nm)
1 micrometer (µm)
1 millimeter (mm)
1 centimeter (cm)
1 meter (m)
1 kilometer (km)
= 1,000 picometers
= 1,000 nanometers
= 1,000 micrometers (=1/100,000 of a meter)
= 10 millimeters
= 100 centimeters = 1,000 mm
= 1,000 meters
Conversions
1 inch (in)
1 centimeter
1 foot
1 meter
1 yard
1 meter
1 chain
1 meter
1 mile
1 kilometer
= 2.54 centimeters (exactly)
= 0.3937 inches
= 30.48 centimeters (exactly)
= 3.28 feet
= 0.9144 meters (exactly)
= 1.0936 yards or 39.37 inches
= 20.1168 meters (exactly)
= 0.0497 chains
= 1.609 kilometers
= 0.621 miles
1 square chain
1 acre (ac)
1 square mile
= 484 square yards
= 10 square chains = 43,560 square feet
= 640 acres
AREA
English
Metric
1 hectare (ha)
= 10,000 square meters
1 square kilometer= 100 hectares
Conversions
1 square meter = 10.76 square feet
1 square yard
= 0.835 meters
1 square chain = 404.6856 square meters
1 acre
= 0.404686 hectares
1 hectare
= 2.471 acres
1 square mile
= 2.5899 square kilometers
1 square kilometer= 0.386 square miles
Seamon: College of Natural Resources, University of Idaho
1
FOR 375 Introduction to Spatial Analysis for Natural Resource Management – UPDATED 12.11.2015
Scale Abbreviations and Formulas
RF
PS
PSR
MS
MSR
GD
MD
PD
ho
representative fraction
MSL mean sea level
photo scale
H
altitude of aircraft above MSL
photo scale reciprocal
DP datum plane
map scale
h
elevation of DP above MSL
map scale reciprocal
H-h altitude of aircraft above DP
ground distance
f
camera focal length
map distance
m meters
photo distance
mm millimeters
difference in height of two points in 3-dimensional space
Basic Scale Formula
PS = f/(H-h), or PSR = H-h/f, or 1/PSR = f/(H-h)
PS = PD/GD, or PSR = GD/PD, or 1/PSR = PD/GD; also MS = MD/GD (for map scale)
PS = PD/(MD x MSR), or PSR = (MD x MSR)/PD, or 1/PSR = PD/(MD x MSR)
Units of Expression
PS, PSR, MSR, to nearest 10 units
h, ho, to nearest foot or 0.1 m
f to nearest inch, .0001' or nearest .001 mm if calibrated
PD, MD to nearest .01" or .1 mm
H, (H-h), GD to nearest 10 ft. or 1 m
Seamon: College of Natural Resources, University of Idaho
2
FOR 375 Introduction to Spatial Analysis for Natural Resource Management – UPDATED 12.11.2015
Significant Figures
In recording measurements, an indication of the accuracy attained is the number of
digits (significant figures) recorded.
By definition, the number of significant figures in any measured value includes the
positive (certain) digits plus one (only one) digit that is estimated or rounded off, and
therefore questionable.
Any properly recorded measurement can be presumed to have a maximum uncertainty
of plus or minus half its last digit.
To be consistent with the theory of errors, it is essential that data be recorded with the
correct number of significant figures. If a significant figure is dropped off in recording a
value, the time spent in acquiring certain precision has been wasted. On the other hand, if
data are recorded with more figures than those that are significant, false precision will be
implied and time may be wasted in making computations.
Two sig. fig: 24, 2.4, 0.24, 0.0024, 0.020
Three sig fig: 364, 36.4, 0.000364, 0.0240
Four sig fig: 7621, 76.21, 0.0007621, 24.00
In multiplication, the number of significant figures in the answer is equal to the least
number of significant figures in any of the factors.
362.56 x 2.13 = 772.2528
772
Seamon: College of Natural Resources, University of Idaho
3