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Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.


r.coin - Tabulates the mutual occurrence (coincidence) of categories for two raster map layers.


raster, statistics


r.coin --help
r.coin [-w] first=name second=name units=string [--help] [--verbose] [--quiet] [--ui]


Wide report, 132 columns (default: 80)
Print usage summary
Verbose module output
Quiet module output
Force launching GUI dialog


first=name [required]
Name of first input raster map
second=name [required]
Name of second input raster map
units=string [required]
Unit of measure
c(ells), p(ercent), x(percent of category [column]), y(percent of category [row]), a(cres), h(ectares), k(square kilometers), m(square miles)
Options: c, p, x, y, a, h, k, m

Table of contents


r.coin tabulates the mutual occurrence of two raster map layers' categories with respect to one another. This analysis program respects the current geographic region and mask settings.

r.coin tabulates the coincidence of category values among the two map layers and prepares the basic table from which the report is to be created. This tabulation is followed by an indication of how long the coincidence table will be. If the table is extremely long, the user may decide that viewing it is not so important after all, and may cancel the request at this point. Assuming the user continues, r.coin then allows the user to choose one of eight units of measure in which the report results can be given. These units are:

percent cover of region
percent of <map name> category (column)
percent of <map name> category (row)
square kilometers
square miles

Note that three of these options give results as percentage values: "p" is based on the grand total number of cells; "x" is based on only column totals; and "y" is based on only row totals. Only one unit of measure can be selected per report output. Type in just one of the letters designating a unit of measure followed by a <RETURN>. The report will be printed to the screen for review. After reviewing the report on the screen, the user is given several options. The report may be saved to a file and/or sent to a printer. If printed, it may be printed with either 80 or 132 columns. Finally, the user is given the option to rerun the coincidence tabulation using a different unit of measurement.


It is not a good idea to run r.coin on a map layer which has a monstrous number of categories (e.g., unreclassed elevation). Because r.coin reports information for each and every category, it is better to reclassify those categories (using r.reclass) into a more manageable number prior to running r.coin on the reclassed raster map layer.


Below is a sample of tabular output produced by r.coin. Here, map output is stated in units of square miles. The report tabulates the coincidence of the Spearfish sample database's owner and road raster map layers' categories. The owner categories in this case refer to whether the land is in private hands (category 1) or is owned by the U.S. Forest Service (category 2). The roads map layer categories refer to various types of roads (with the exception of category value "0", which indicates "no data"; i.e., map locations at which no roads exist). r.coin does not report category labels. The user should run or r.category to obtain this information.

The body of the report is arranged in panels. The map layer with the most categories is arranged along the vertical axis of the table; the other, along the horizontal axis. Each panel has a maximum of 5 categories (9 if printed) across the top. In addition, the last two columns reflect a cross total of each column for each row. All of the categories of the map layer arranged along the vertical axis are included in each panel. There is a total at the bottom of each column representing the sum of all the rows in that column. A second total represents the sum of all the non-zero category rows. A cross total (Table Row Total) of all columns for each row appears in a separate panel.

Note how the following information may be obtained from the sample report.

In the Spearfish data base, in area not owned by the Forest Service, there are 50.63 square miles of land not used for roads. Roads make up 9.27 square miles of land in this area.

Of the total 102.70 square miles in Spearfish, 42.80 square miles is owned by the Forest Service.
In total, there are 14.58 square miles of roads.

There are more category 2 roads outside Forest Service land (2.92 mi. sq.) than there are inside Forest land boundaries (0.72 mi. sq.).

Following is a sample report.

|                    COINCIDENCE TABULATION REPORT           |
|Location: spearfish    Mapset: PERMANENT   Date: Wed Jun 1  |
|                                                            |
| Layer 1: owner          -- Ownership                       |
| Layer 2: roads          -- Roads                           |
| Mask:    none                                              |
|                                                            |
| Units:   square miles                                      |
| Window:                North: 4928000.00                   |
|          West: 590000.00               East: 609000.00     |
|                        South: 4914000.00                   |

Panel #1 of 1
|        | owner                 |    Panel Row Total    |
|   cat# |         1 |         2 |   w cat 0 | w/o cat 0 |
|r     0 |     50.63 |     37.49 |     88.12 |     88.12 |
|o     1 |      1.53 |      0.68 |      2.21 |      2.21 |
|a     2 |      2.92 |      0.72 |      3.64 |      3.64 |
|d     3 |      3.97 |      2.57 |      6.54 |      6.54 |
|s     4 |      0.65 |      1.36 |      2.00 |      2.00 |
|      5 |      0.19 |      0.00 |      0.19 |      0.19 |
|Total   |           |           |           |           |
|with 0  |     59.90 |     42.80 |    102.70 |    102.70 |
|w/o 0   |      9.27 |      5.32 |     14.58 |     14.58 |

|        |    Table Row Total    |
|   cat# |   w cat 0 | w/o cat 0 |
|r     0 |     88.12 |     88.12 |
|o     1 |      2.21 |      2.21 |
|a     2 |      3.64 |      3.64 |
|d     3 |      6.54 |      6.54 |
|s     4 |      2.00 |      2.00 |
|      5 |      0.19 |      0.19 |
|Total   |           |           |
|with 0  |    102.70 |    102.70 |
|w/o 0   |     14.58 |     14.58 |

r.coin calculates the coincidence of two raster map layers. Although r.coin allows the user to rerun the report using different units, it is not possible to simply rerun the report with different map layers. In order to choose new map layers, it is necessary to rerun r.coin.


g.region, r.category, r.describe, r.reclass,, r.stats


Michael O'Shea,
Michael Shapiro,
U.S. Army Construction Engineering Research Laboratory


Available at: r.coin source code (history)

Latest change: Thursday Feb 03 11:10:06 2022 in commit: 547ff44e6aecfb4c9cbf6a4717fc14e521bec0be

Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

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