The Top Nine Reasons to Use a File Geodatabase Continued from page 13 Number/Type of features 7,118,614 lines 8,205,055 points 383,531 lines 285,285 points 319,000 polygons 232,375 polygons Compression ratio (1:x) 4.5 4.4 3.4 2.8 2.4 1.4 Sample data Germany streets U.S. census blocks Europe rails Calgary addresses Calgary buildings Europe water Number of fields 83 11 12 8 9 10 Uncompressed size 2.3 GB 705 MB 58 MB 21 MB 48 MB 176 MB Compressed size 511 MB 162 MB 17 MB 7.4 MB 20 MB 125 MB Effects of compression by feature type and numbers Compression is ideally suited to mature datasets that do not require further editing. However, if required, a compressed dataset can always be uncompressed and returned to its original, read/write format. The compression method applied is lossless, so no information is lost. One of the most important factors affecting spatial data compression is the average number of vertices per feature. As a general rule, the fewer vertices/features, the greater the compression. The tables above illustrate the effects of applying compression. Ready to Try File Geodatabases? The file geodatabase provides a widely available, simple, and scalable geodatabase solution for all users that can work across operating systems. It can scale up to handle very large datasets and still provide excellent performance. Its efficient data structure is optimized for performance and storage and uses about one-third the feature geometry storage required by shapefiles and personal geodatabases. File geodatabases also allow users to compress vector data to a readonly format that further reduces storage requirements. Keyword name DEFAULTS TEXT_UTF16 MAX_FILE_SIZE_4GB MAX_FILE_ SIZE_256TB Keyword setting 1 TB 1 TB 4 GB 256 TB Usage Default settings Optimizes storage for non-Latin alphabet text Restricts dataset to a maximum size of 4 GB; stores datasets less than 4 GB more efficiently than DEFAULTS keyword Used to create a dataset that is up to 256 TB in size Keywords for customizing data storage Action Create empty feature class. Add/Create features in empty feature class. Add different-sized features to feature class. Load data using simple data loader or Append tool. Import data. Copy/Paste feature class personal to a file geodatabase. Copy/Paste feature class from file or ArcSDE geodatabase. Compress data. Uncompress data. Effect on spatial index Spatial index is created, but remains in unbuilt state. Grid sizes are set to 0,0,0. Initial grid sizes 0,0,0 are automatically rebuilt as feature properties are updated. Manually update the index. The Indexes tab appears in the Feature Class Properties dialog box. Click the Recalculate button. The spatial index is built as the final step of the loading process. Appropriate grid sizes are calculated for the new added features. The spatial index is automatically computed for the new feature class. The spatial index is automatically rebuilt. The spatial index is copied from the source, not recomputed. An alternate indexing method is automatically applied and cannot be modified. Precompression index is automatically reestablished. File geodatabase and spatial indexes table 14 ArcUser Spring 2009 www.esri.com