Why limited the length of field to 10?

[kuno]

I am new to shapefile, I saw in this line of code
https://github.com/GeospatialPython/pyshp/blob/master/shapefile.py#L744

That you limited the lenght of the field to 10 at most, can you explain why?

[GeospatialPython]

The Dbf format limits fields to 10 characters. There are some derivative
formats that try to work around this limitation, but nearly all GIS
software truncates Dbf files to 10.

Some GIS software will handle longer fields with different database
formats. But shapefiles have a hard limit.

• Joel

On Monday, June 30, 2014, kuno notifications@github.com wrote:

I am new to shapefile, I saw in this line of code
https://github.com/GeospatialPython/pyshp/blob/master/shapefile.py#L744

That you limited the lenght of the field to 10 at most, can you explain
why?

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Reply to this email directly or view it on GitHub
#2.

Joel Lawhead, PMP
E-mail: jlawhead@geospatialpython.com
Web: GeospatialPython.com http://geospatialpython.com/
Twitter: @SpatialPython

[kuno]

ok, very helpful.

Thanks.

[jinz2014]

Dear Author,

In the dbf file format https://en.wikipedia.org/wiki/.dbf, the size of the field name is 11 bytes, not 10 bytes. Could it be fixed if it is a bug ?

Database field descriptor bytes

0-10 11 bytes Field name in ASCII (zero-filled)

Thank you for reading and reply.

[eldang]

@jinz2014 the shapefile article spells out that the maximum length of a field name is only 10 characters. I don't know what the 11th byte is used for, but it's existence doesn't allow shapefiles to have 11 character field names.

It may be possible to hack something that lets people use longer field names within pyshp, but this stack exchange thread makes clear why that would be a bad idea.

[micahcochran]

In DBF the 11th byte is a zero (00h) value, for null termination. It is probably the way to make seem to be somewhat like C null terminated strings. You might be able to use fscanf to read it in, which almost nobody would do today. Remember, dBase is a DOS format with design decision made back in the 1980s.

It is not a bug, its a feature! 😄

ESRI's ArcGIS software has aliases for field, which I assume is just in the map .MXD file for display to the end user.

[jinz2014]

Thank you for your answer.

From: Eldan Goldenberg [mailto:notifications@github.com]
Sent: Wednesday, March 23, 2016 3:27 PM
To: GeospatialPython/pyshp
Cc: JIN, ZHEMING
Subject: Re: [pyshp] Why limited the length of field to 10? (#2)

@jinz2014https://github.com/jinz2014 the shapefile articlehttps://en.wikipedia.org/wiki/Shapefile#Data_storage spells out that the maximum length of a field name is only 10 characters. I don't know what the 11th byte is used for, but it's existence doesn't allow shapefiles to have 11 character field names.

It may be possible to hack something that lets people use longer field names within pyshp, but this stack exchange threadhttps://gis.stackexchange.com/questions/15784/how-to-bypass-10-character-limit-of-field-name-in-shapefiles makes clear why that would be a bad idea.

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