User:Jeisenbe/Waterway Widths

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  • On May 30 to 31st, 2019, I checked the count of all rivers, streams, canals, ditches and drains in OSM tagged with width=*. An analysis for this data follows.


  • ditches, drains and streams are almost always narrow waterways:
    • 80% are less than 2 meters wide and over 90% are less than 5 meters wide.
    • Alhougth some streams are wider, less than 5% are over 10 meters
  • Rivers are wider, although there is some overlap with streams at 2 to 5 meters.
    • Almost 95% of rivers are 2 meters or wider
    • 85% of rivers are wider than 3 meters.
    • Almost half of rivers are wider than 10 meters.
  • The tag waterway=canal has a wider range of widths
    • 85% of canals are 2 meters or wider and 26% are wider than 10 meters
    • But there are over 2000 canals with width of 1 meter or less (2.8% of all canals with a width tag)
    • Only a small number of features are tagged as for irrigation, but most of these are canals, even at the smallest widths
  • Mappers might want to discuss better ways to tag canals differently. Renderers and database users might appreciate more width tags for canals.

Go look at the pretty charts and tables below:

Analysis of Waterway Widths

Current definition of Waterways

The two main tags for natural waterways, waterway=river and waterway=stream, are distinguished by the width of the watercourse:

  • a stream is "A naturally-forming waterway that is too narrow to be classed as a river (the commonly accepted rule for OpenStreetMap is that a stream can be jumped across by an active, able-bodied person).
  • a river is a "linear flow larger natural waterway"

However, the three main tags for artificial waterways are less clearly distinguished, mainly by usage but partially by width:

  • waterway=canal is "an artificial open flow waterway used to carry useful water for transportation, waterpower, or irrigation."
  • waterway=drain is an "artificial waterways, typically lined with concrete or similar, used to carry superfluous water like storm water or grey-discharge"
  • waterway=ditch is used for "simple narrow artificial waterways used to drain nearby land, to remove storm-water or similar"


The definitions above suggest that only waterway=canal is appropriate for watercourses designed for irrigation. But the current tags that specify waterway use are also used for waterway=ditch and waterway=drain.

This is inconsistent with the usage of the word "ditch" in some dialects of English, where it is common to speak of a small unlined irrigation waterway as an "irrigation ditch".

  • irrigation=yes was the first tag used, starting it 2011. As of May 2019, it has been used 200 times with canals and 2000 times with ditches. Most of these tags were added between 2011 and 2013.
  • service=irrigation was used starting in 2012, and as of May 2019 is used 12,000 times
  • usage=irrigation was introduced in 2018 and usage is increasing quickly. It is currently used 6,000 times.

A search of the database on 2019-May-30 shows 10,519 waterway=canal with one of these 3 tags But 3,673 waterway=ditch have one of the irrigation tag, and even 1,300 waterway=drain have a tag for irrigation usage (though "drain" usually refers to wastewater in plain English).

Influence of rendering

  • The main style on - know as Openstreetmap-Carto - currently renders rivers at an earlier zoom level than streams, and when both are rendered the rivers shown with a wider line.
  • Canals are also rendered with a wider line and at an earlier zoom level than the other artificial waterways - drains and ditches
  • At the moment drains are rendered slightly narrower than ditches
  • These rendering results suggest to mappers that ditches and drains are narrower than canals

Recent discussions

On the tagging list, we have recently discussed if there is a need for a new type of waterway, for narrow irrigation channels, instead of waterway=drain or waterway=canal. It has also been discussed if waterway=ditch or even waterway=drain can be appropriately used for irrigation waterways.

Analysis of currently tagged waterway widths

To review how the tags I currently used, I checked how many OSM ways (linear features) were tagged with a combination of waterway=* and width=* as of May 30th 2019. Since it isn't possible to directly download a range of width values, I checked each number from 1 to 15 separately, and also checked for strings that started with "0.", "1." etc to find decimals. Normally these width values should be in meters, although it is apparent that there are some mistakes.

This analysis is only able to review the minority of waterways which have been tagged with a specific width, but it is hoped that these examples are somewhat consistent with general use of the tags by mappers.

Raw Data

Zip with .csv files

Zip with .xlsx file including calculations and charts


On May 30th and 31st, 2019, I used to search for each combination of width and waterway:

Example query for canals with width of 1.* (that is, the width tags begins with “1.” - this includes all widths from 1.000… to 1.999…).

 out count;

I then entered each value from “.*” and “0.*” to “11.*” in a spreadsheet. I also checked the integer values up to 15, then every 5 meters up to 30, plus 50 and 100.

Due to some suspicious data in the values above 10 (presumed to be in meters), I checked these by downloading the complete data for drains and ditches tagged with width=15, width=50 and =100 - I noted that about half of these were clearly imported data that was intended to be in “cm” or another unit, and some of the others were too short of ways to be reasonably interpreted as >15 meter wide waterways, therefore I did not include this data in the analysis of artificial waterways. This issue may also affect streams with width >10 to some extent.

The data is available in the zip files above. The xlsx format spreadsheet also shows the calculations performed.

The percentage of each type of waterway at a certain width was calculated.

Charts were also made comparing the 3 main types of artificial waterway: waterway=canal, waterway=ditch and waterway=drain

Other charts were produced comparing the 2 types of natural watercourse: waterway=river and waterway=stream.

I also specifically checked the features tagged as being used for irrigation with the tags irrigation=yes, service=irrigation or usage=irrigation

Example query used: [1]


This is probably the most important table. It shows what percentage of each feature is tagged with a with less than a certain number of meters.

Width waterway=stream waterway=river waterway=drain waterway=ditch waterway=canal
Number with width 74652 24830 13933 11012 15907
% < 1 m 14% 0.4% 38% 20% 2.8%
% </= 1m 42% 3.4% 65% 59% 13%
% < 2 m 46% 5.5% 74% 63% 15%
% </= 2m 81% 12% 83% 84% 29%
% < 3 m 82% 15% 84% 85% 30%
% < 5 m 92% 36% 91% 93% 52%
% </= 5m 94% 45% 93% 95% 61%
% < 10 m 96% 55% 94% 97% 74%
% width >/= 10 m 4.5% 45% 5.8% 3.1% 26%

In bold are the points where a majority of features of that type are included; eg a over 2/3rds of waterway=stream features with a {{width=*` tag are less than or equal to 2 meters in width, while almost half of rivers are greater than or equal to 10 meters in width.

- 2/3rds (67%) of streams are 1 m to 2 m wide

- Note that over half of waterway=ditch and waterway=drain are less than or equal to 1 meter in width

- In contrast, almost half of waterway\canal=* are wider than 5 meters.

In italics is the 90th percentile, both at the larger and smaller end, when available.

Note that the over 10% of streams, drains and ditches are less than 1 meters in width (0.9* and less), and in fact 38% of drains, and 20% of ditches, are tagged with this small of a width!

In contrast, only 5.5% of rivers are less than 2 meters in width, and less than 13% of canals are 1 meters width or less.

However, in contrast to rivers, there are a small but significant number of canals with 1 meter width and even almost 3% with sub-meter width tagging.

On the larger end, streams, ditches and waterways all have 91% to 93% of widths less than 5 meters (I've checked some of small number of ditches and drains tagged with width > 10, and many appear to be mistakes where the unit is in centimeters or perhaps inches rather than meters)

Both canals and rivers are commonly found in much larger widths: 26% of canals and 45% of rivers with a width tag are wider than 10 meters.

So it appears that ditches and drains are features with a similar size to waterway=stream features, although on the small end there are many more sub-meter width drains and ditches with a width tag than streams (probably since it is hard to measure the width of a natural stream to decimeter precision!)

But canals are not entirely like rivers, because while rivers are never used for tiny waterways, there are some tiny artificial waterways tagged as canals

Compare these two charts:

On the one hand, mappers are more consistent in tagging a 10 meter wide artificial waterway as a canal instead of a ditch or drain - at this width there are still a surprisingly high number of streams instead of rivers (even though the world long jump record is less than 9 meters).

But on the other end of the scale, there are still a number of tiny canals.


As mentioned above, I downloaded each of the 5 types of waterway which was also tagged with one of the tags that specifies usage for irrigation

There are 10519 waterway=canal, 3673 waterway=ditch and 1300 waterway=drain with one of these tags, but only a small percentage also have a width= tag: 1241 waterway=canal, 140 waterway=ditch and only 3 waterway=drain

Unsurprisingly, with those topline numbers there are more waterway=canal at each width, though waterway=ditch gets close at the smaller widths.

But considering that the ration is 3 to 1 (canals to ditches) with irrigation tags, there may be nearly equal numbers of narrow ditch and canalf eatures, were they tagged consistently:

Irrigation-Canal & Ditch + Width - 100% totals

[File:Https:// Irrigation Canals vs Ditches Cumulative percentage]

Certainly it looks like many mappers consider waterway=ditch appropriate for use with irrigation channels, and not only for drainage ditches. But waterway=drain is clearly a very uncommon tag for irrigation features.


  • Database users can be confident that ditches, drains and streams are almost always narrow waterways, usually less than 3 meters wide and almost always less than 5 meters (though some streams are wider).
  • It might be beneficial to render waterway=* less than 1 meter wide differently: this is a large minority of all drains and ditches with a width tag, but > 85% of streams are over a meter in width. Instead of rendering all ditches and drains thinner, one could render them at the same width as streams normally, but thinner if under 1 meter width is tagged.
  • The majority of streams are between 1 and 2 meters width, and almost all streams, ditches and drains are less than 5 meters width, so this should be kept in mind when making rendering decisions.
  • Rivers are usually 3 or more meters in width (although 2 meters is quite common): 3 meters is the most common tag, at 13.4% of all waterway=river + width combinations.
  • Almost half of tagged rivers are > 10 m width
  • Canals have a wide distribution: 14% of canals are 2 meters wide, and 13% are 3 meters wide, but about 13% are 1 meters or less, versus 26% that are greater than 10 meters wide.
  • This suggests that canals would benefit most from a width-specific rendering, or more specific sub-tags
  • Most features tagged as being used for irrigation are canals, but there is a significant minority of waterway=ditch with these tags, especially at the narrower widths (< 2 meters). It seems that not all users are comfortable tagging small irrigation channels as waterway=canal but waterway=ditch is used infrequently for irrigation features
  • It may or may not be beneficial to have a specific tag for small waterways that are used for irrigation or drinking water or other useful purposes, like aqueducts, lavadas, leats, mill races, flumes, etc. - alternately some additional subtags for waterway=canal may be needed along with more consistent use of width=* for narrow features.