{"id":8188,"date":"2019-02-27T00:30:49","date_gmt":"2019-02-26T23:30:49","guid":{"rendered":"http:\/\/www.sigterritoires.fr\/?p=8188"},"modified":"2019-02-27T08:42:52","modified_gmt":"2019-02-27T07:42:52","slug":"job-optimization-with-arcgis-geodatabases-2-compression","status":"publish","type":"post","link":"https:\/\/www.sigterritoires.fr\/index.php\/en\/job-optimization-with-arcgis-geodatabases-2-compression\/","title":{"rendered":"Job optimization with ArcGis Geodatabases: 2-Compression"},"content":{"rendered":"\n

The different\ntypes of geodatabases<\/strong> <\/p>\n\n\n\n

A little reminder before continuing, there is not just one\ngeodatabase but several. There are personal geodatabases\nand enterprise geodatabases.
\nPersonal\ngeodatabases can be created with ArcCatalog in your computer, or in a network\ndrive. There are two available formats: the personal geodatabase\nthat uses an Access format and the file geodatabase that uses an ESRI brand\nformat.
\nTo\ncreate an enterprise geodatabase you will need to use ArcSDE and the format\ndepends on the DBMS being used (Oracle, for example).
\nIn\nthis article, we will not discuss the enterprise geodatabases.
\nWhile\nthere are two formats of personal geodatabases, we will discuss the file geodatabases\nbecause the access databases just maintain compatibility with the old\ngeodatabases. Indeed, the geodatabase of the\nArcGis first version used the format Access, but the use constraints (limitation\nto 2Go for the size, etc) led ESRI to develop its own format. Currently\nthere is no valid reason to keep on creating access geodatabases.\n
\nIt\nis rather important not to confuse the compression of a file geodatabase with\nthe compression of an enterprise geodatabase (which is outside the scope of\nthis article). Compressing a file geodatabase\ndoes not delete the data it contains. However,\nit prevents the content from being updated. <\/p>\n\n\n\n\n\n\n\n

Compression of a file\ngeodatabase<\/strong> <\/p>\n\n\n\n

Do not confuse compression and compaction. We\nwill discuss compaction in a next article (Job optimization with ArcGis 3-\nGeodatabases Compaction). Compressing a geodatabase is\nlike compressing an image: the only goal is to save disk space by reducing its\nsize.
\nWhen\ncompressed, the geodatabase is marked as read-only. This\nmeans that you will not be able to perform any editing operation on the\ngeodatabase. If you try to use ArcMap to\nmodify it, you will get a message saying there is no editable layer and that\nthe geodatabase is compressed.
\nTo\ncompress a file geodatabase, perform the following steps:
\n1. Open ArcCatalog.<\/strong>
\n2. Locate and right-click the file geodatabase, check\nAdministration, and then click Compress file geodatabase.<\/strong>
\nYou\nwill notice the existence of the inverse command (Uncompressing a file\ngeodatabase) that allows to restore the original geodatabase and to edit it.\n
\nThe\nonly option in the Compression window is a \u00ab\u00a0Lossless Compression\u00a0\u00bb\ncheck box.
\nThe\ncompression operation may be performed with or without loss of data.\nLoss compression was the only option available before ArcGIS\n10.0 file geodatabases. For geodatabases that run on\nversions 10 and later, you have two options: lossless and loss compression.\n
\nDo\nnot ask me what can be used for data loss compression, for a database manager\nit’s heresy!
\nLoss compression<\/strong> is the process by which the content\nis compressed while losing some of its content. It’s\nan irreversible operation. This is what can be done with\nimage compressions where, from a certain degree of compression there has been\nlost some definition of the image. On\nthe other hand for attributesdata it is absolutely necessary to avoid this type\nof compression.
\nLossless compression<\/strong> compresses the content while\npreserving the data. It’s a reversible operation.\n
\nCompression\ncan be used to save a lot of disk space, especially for geodatabases with a\nlarge number of entities. If the geodatabase is mature\nenough and has not been modified for a long time, it is advisable to use\nlossless compression to reduce its size.
\nBefore\nusing compression, always remember to create a backup of your file geodatabase.\nCompression can sometimes corrupt the geodatabase and make\nit inaccessible.<\/strong>
\nFor\nmore information on how to compress ArcGis geodatabases, visit the ArcGis\nOnline Help (ESRI)<\/a> <\/p>\n","protected":false},"excerpt":{"rendered":"