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Clean makes .MAP bigger

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  • 1.  Clean makes .MAP bigger

    Posted 11-22-2018 19:14
    I have observed some unusual behaviour with the Clean command.
    I am running MapInfo 64-bit version 16.0.3

    I have a table containing one record, a very large polygon, which is the result of buffering railway tracks.
    The original .MAP had a file size of 5,789 KB
    The original polygon had 728,840 nodes

    I ran the Clean command on the table (without the Overlap or Gap Area keywords)

    The new .MAP had a file size of 11,455 KB
    The new polygon had 713,647 nodes

    The change in number of nodes does not worry me. It is almost the same, and is easily explained by being a result of cleaning.
    But, why has the .MAP file doubled in size? The number of nodes has not doubled. Is there something different in the way the geometry has been stored?

    Nick Lawrence

  • 2.  RE: Clean makes .MAP bigger

    Pitney Bowes
    Posted 11-22-2018 20:00
    Hi @Nick Lawrence - quick question: have you tried running a Pack table after the clean & did this change the size of the .MAP file  ?

    Ashley Crane
    Regional Director, Software Support
    Pitney Bowes

  • 3.  RE: Clean makes .MAP bigger

    Posted 11-22-2018 20:51
    I ran Pack and it went back to the original size.

    Nick Lawrence
    TMR-Policy and Planning

  • 4.  RE: Clean makes .MAP bigger
    Best Answer

    Pitney Bowes
    Posted 11-22-2018 23:04
    Thanks Ashley.
    And Nick, this behavior is by design and as expected. The doubling in size result is an extreme case given your file on has one large polygon. The clean operation does nothing to a polygon if no cleaning is required. In your case the one polygon needed cleaning and inside the file the old version of the polygon is flagged as deleted and the new version is added. It works this way for execution efficiency and safety. Hence the size increase and why the pack operation restored the file to about its original size.

    Steven Mann
    Pitney Bowes Software Pty Ltd
    Macquarie Park