Ask A Cartographer

Real life line widths

July 22 2008 | 1 comment
Categories: Cartographic Effects, Map Data, Symbology

I have a line layer of streets. I would like to have one of the streets, only on some maps, resemble the real street width, in meters. How can I do this, short of creating a polygon of the street. I really just want to use the line layer and set the width of the line to represent the width of the street. The other issue is the maps will be in different sizes and scales, so each map I want to lesson the actions I must take to represent the real width.
Thank you

Mapping Center Answer:

First you need an attribute in your street lines data that contains the width of the street. If you don't have that attribute, then you'll be depending on other attributes that typically were not intended to be used in the fashion you're after, such as 'Street Class'. The reason attributes like 'street class' are problematic is that they don't account for parking, medians, dedicated turn lanes, bicycle lanes, shoulders, etc.

If you've got that attribute, then you can use the symbology method called Proportional Symbols (on the Layer Properties dialog, on the Symbols tab, it is available in the Quantities section). Here, the only requirement is that your data be projected. My guess is you'll want to be using either a UTM or State Plane coordinate system for best results (just using a GCS, e.g., WGS84, will become problematic as the location for your map moves away from the Equator).

Just select your street width field and then set the units--the reason you need a projection is so ArcMap can translate the data's units to the coordinate system's units.

The tricky part is that most street centerline data is not broken up on the basis of street widths (I've tried doing this not to long ago with mixed results). The problem is one of left-side versus right-side, i.e., a bike lane on the left and then an indented curb for parallel parking occuring infrequently on the right. The solution I went with instead was to buffer the road lines based on width class, i.e., our area has roads that are 30, 36, 45, etc. feet wide. Then I used imagery to adjust the widths to reflect the details in the curbs, but only had to do so when irregularities occurred--I predominanty used the reshape and modify editing tasks to do that work (note when you use the link for reshape, see the contents at the left for help on the other edit tasks).

The only issue with this approach was needing a really good street centerline dataset to base the buffers on (I found it was useful to edit the street centerlines using the Reshape task to insert true curves, which then made the buffers look really nice).

coordinate systems posted by Aileen Buckley on Jul 23 2008 1:27PM
Just a quick clarification -- the UTM grid coordinate system is a worldwide system so this may be useful for you if you are mapping an area less than 6 degrees wide in longitude (and hopefully you are not at the edge of two UTM zones). The State Plane grid coordinate system is a system for the U.S. only. Other countries may also have grid coordinate systems designed specifically for the territory they cover.

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