About distance units and editing

When editing, the map units of your data frame are used when reporting and entering measurements and distances. The map units are the units in which the spatial data in the data frame is drawn. The map units are determined by the coordinate system of the data frame. When editing, all the values you enter will be in map units by default. You can find out the map units used by your coordinate system on the Data Frame Properties dialog box > General tab.

Sometimes when creating features, you need to enter values that were recorded in different distance units than the coordinate system of your data. When you input measurements, in many cases it is possible to enter values in units other than map units by specifying a units abbreviation with the value.

For example, suppose your data is in a State Plane coordinate system and the linear units are U.S. survey feet. You are given measurements in meters. Rather than convert all the measurements to U.S. survey feet, you can type the abbreviation for meters, m, after the measurements, and the tools will convert the distance correctly.

Whenever you are typing a distance into one of the editing tools, you have the option to specify the linear units or simply type a number, which the tool will interpret as being in map units. Unit abbreviations only work when your data frame uses a projected coordinate system rather than a geographic coordinate system.

The following sections outline all the unit abbreviations supported when editing and describe how to implement them.

Metric units

Distance units

Abbreviation

Meters per unit

Description

Kilometer

km

1,000

1,000 meters exactly

Meter

m

1

International meter

Centimeter

cm

.01

1/100 meters exactly

Millimeter

mm

0.001

1/1000 meters exactly

Metric units

Imperial or international units

Distance units

Abbreviation

Meters per unit

Description

Foot

ft

0.3048

Also known as international foot or imperial foot that was used in most non-U.S. countries before the metric system.

Mile

mi

1,609.344

Also referred to as a statute mile, equal to 5,280 international feet.

Nautical mile

nm

1,852

The nautical mile is a unit of distance used primarily in sea travel and aviation. The nautical mile is defined as the average distance on the earth's surface represented by one minute of latitude. In 1929, the nautical mile was defined as exactly 1,852 meters, or 6,076.11549 feet, a distance known as the international nautical mile.

Chain

ch

20.1168

66 international feet.

Yard

yd

0.9144

3 international feet.

Rod

rd

5.0292

1/4 chain, or 16.5 international feet.

Link

lk

0.201168

1/100 international chain, or 66/100 international feet.

Inch

in

0.0254

1/12 international feet.

Imperial or international units

U.S. survey units

Distance units

Abbreviation

Meters per unit

Description

Survey foot

ftUS

0.3048006096

The U.S. survey foot is used in the state plane coordinate systems. In the United States, fundamental survey units, such as rods, chains, statute miles, acres, sections, and townships, all depend on the U.S. survey foot. An exact conversion to meters can be accomplished by multiplying U.S. survey feet by the fraction 1,200/3,937.

Survey mile

miUS

1,609.3472186944

5,280 survey feet.

Survey chain

chUS

20.1168402337

66 survey feet.

Survey rod

rdUS

5.0292100584

1/4 survey chain.

Survey link

lkUS

0.2011684023

1/100 survey chain.

Survey yard

ydUS

0.9144018288

3 survey feet.

U.S. survey units

Entering specific locations (DD, DMS, DDM, MGRS, USNG, and UTM)

In commands that require you to enter a specific location when editing, you can specify the location as a longitude-latitude coordinate pair, a Military Grid Reference System (MGRS) grid location, a U.S. National Grid (USNG) location, or a Universal Transverse Mercator (UTM) coordinate. Map units are the default, but you can click the Units button Units to choose the units in which to enter coordinates.

These are the same formats used by the Go To XY command. Below are some guidelines for specifying these values. These apply to Absolute XY and commands such as Move To that allows you to move a vertex or topology element to an exact location.

Valid longitude-latitude inputs

-45

-45

45 W

45 S

45.50W

45.50S

W45

S45

45 30.5W

44 30.5S

45° 30'30"W

45°30'30"N

45 30 30 W

45 30 30 N

-45 30 30

45 30 30

45 30.50W

45 30.50

-45.50833

45.50833

Valid MGRS and USNG inputs

18SUH

100,000-meter square

0-digit coordinate

18SUH64

10,000-meter square

2-digit coordinate

18SUH6743

1,000-meter square

4-digit coordinate

18SUH678432

100-meter square

6-digit coordinate

18SUH67894321

10-meter square

8-digit coordinate

18SUH6789043210

1-meter square

10-digit coordinate

Valid UTM coordinate notation input

17R 419230 2714967

1-meter square

13-digit coordinate

Conversion constants

You can use conversion constants to convert from one measurement system to another. The measurement system to be converted should be multiplied by the associated conversion constant. For example, to convert feet to centimeters, multiply feet by the conversion constant of 30.48 (27 feet x 30.48 = 822.96 centimeters). For a list, refer to the PDF of conversion constants.

If this link does not work, you can open the conversion_constants.pdf from the \Documentation folder in the directory where you installed ArcGIS. To view this document, you need a copy of Adobe Reader.

About the U.S. survey foot

In 1959, the directors of the National Bureau of Standards and the United States Coast and Geodetic Survey agreed on a redefinition of the inch-centimeter relationship. This redefinition defined 1 inch as equal to 2.54 centimeters exactly, or 1 foot as equal to 0.3048 meters exactly. However, their agreement stipulated that the older value for 1 meter equaling 39.37 inches exactly be retained for identifying the U.S. survey foot.

One of the reasons for this retention was that the state plane coordinate systems, which are derived from the national geodetic control network, are based on the relationship of 1 meter equaling 39.37 inches exactly.

The difference between these two values for the foot is very small, two parts per million, which is hardly measurable, but not trivial when computational consistency is desired. Fundamental survey units, such as rods, chains, statute miles, acres, sections, and townships, all depend on the relationship of 1 meter equaling 39.37 inches exactly.

The U.S. survey foot table represents the corrected values (or U.S. survey values), using the 39.37-inch conversion value.

Related Topics

10/24/2012