# Converting Between Scale Types of Historic & Topographic Maps, page 1

## Converting Bar Scale to Representative Fraction (RF)/Ratio Scale

### English and Metric **Measures of Length** to use:

**1 inch (in)** = 2.54 centimeters

**1 centimeter (cm)** = 0.39 inch

**1 foot (ft)** = 12 inches = 30.5 centimeters = 0.3 meter

**1 yard (yd)** = 36 inches = 3 feet = 91.44 centimeters = 0.9 meter

**1 meter (m)** = 100 centimeters = 39.37 inches = 3.28 feet = 1.09 yards

**1 mile (mi)** = 63,360 inches = 5,280 feet = 1,760 yards = 1.609 kilometers

**1 nautical mile** = 1,852 meters = 1.852 kilometers

**1 kilometer (km)** = 1,000 m = 100,000 cm = 1,094 yards = 0.6 mile

NOTE: When you carry out any calculation with fractions, make sure that all units in equation are cancelled correctly. If necessary, invert the RF for that purpose.

If the map that I am going to use for my research has a Bar Scale, I can easily determine the map's scale expressed in small units.

First, I take a measurement from the bar scale to determine the map distance that corresponds to a ground distance. By measuring with a compass or just a ruler, I find that 10 kilometers measures 2.5 cm.

I use this relationship (2.5 cm to 10 km) for determining the map's scale which will show how many centimeters on the ground are represented by one cm on the map:

**or 1:400,000**

**1)** A simple formula for converting Bar Scale to RF Scale in **Metric units** looks like this:

**step 1:**

**step 2:**

where:

**RF **- Representative Fraction Scale of the map,

**A (cm)** - actual distance - a number of centimetres on the ground surface, represented by 1 centimetre (1 cm) on a map,

**B (km)** - value of one small incriment of a Bar Scale,

**C (cm)** - length of the "B" incriment measured on a Bar Scale.

**2)** A similar formula for converting Bar Scale to RF Scale in **English units** looks like this:

**step 1:**

**step 2:**

where:

**RF ** - Representative Fraction Scale of the map,

**A (inches)** - actual distance - a number of inches on the ground surface, represented by 1 inch (or 1") on a map,

**B (miles)** - value of one small incriment of a Bar Scale,

**C (inches)** - length of the "B" incriment taken from a Bar Scale.

| Converting Bar Scale to RF/Ratio Scale | Converting RF/Ratio Scale to Lexical Scale |

| Converting Lexical Scale to RF/Ratio Scale | **Next >**

**Back to Basic Calculations for Map Research page**

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