I am converting an .xls file (500kb) to a .csv (150KB) then using this to generate a MapInfo .tab file format using both QGis and ArcGIS. I can use an intermediate file ie. mif/mid format which gives a file size of about 250KB in both cases however when I convert this to .tab format I get a .dat file of about 6MB (the .id, .map and .tab total 14KB) using both programs. Note that QGis will not allow me to generate the .tab without generating a .mif first. Zipping these for emailing drops the size from about 6MB to less than 500KB so lot of empty space somewhere.

Have looked within the text files (.csv and the .mif/mid) but see no issues. I have used this method before on an older versions of this.xls file to generate MI format files totaling less than half a meg without any issues.

Any suggestions as to what is going on? Currently have no access to MapInfo to try.

  • 1
    What's about the data type? Maybe all columns are handled as 254 Byte long strings resulting in huge, but rather empty files. This would explain the compression rate.
    – Detlev
    Jan 28, 2016 at 7:13
  • If this is the case, any idea on how to check or how to control header data type in a .dat? I always assumed this was automatic. It must be something to do with contents but this is not really my area of expertise. I can open the .dat in Notepad++ but not really sure what I'd look for,
    – DirkB
    Jan 29, 2016 at 5:25
  • As KWadg I would like to inspect the file. Sometimes I had trouble with Excel tabs having column headers in the first lines, or all rows get exported even if they were empty, or decimal seperator issues. Just to name a few. Since .dat is binary it's hard to edit something. Just now I have no example at hand but I think that .tab contains the table structure with field defs
    – Detlev
    Jan 29, 2016 at 6:27

1 Answer 1


I don't know how much or what type of information you have in your .CSV, but I looked at files of mine which for instance hold over 500,000 streets (polylines) where the .DAT file is 90MB and another file with 2,500 cities (polygons) where the .DAT file is only 400KB. If you'd like to send me the .CSV I can covert it to .TAB for you through MI and see if I get the same results.

  • Thanks for offer. File is small 60 rows, 60columns. I have actually sent it to a friend of mine to convert to MI to see if still same issue when doing this in the native application. Will let you know result and if needs more investigation.
    – DirkB
    Jan 29, 2016 at 5:18
  • Correction: 400 rows, 60 columns. Only point data.
    – DirkB
    Jan 29, 2016 at 5:24
  • As @Detlev said in his comment above, it might be in the definition of what type of variable each column is. But it is hard to answer off hand without the info. Looking forward to the update after your friend coverts it.
    – KDawg
    Jan 29, 2016 at 13:56

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