# Check for Direct Links to Data

This FGDC conformance check verifies that links to a zip file contain geospatial data. 

## Direct Data Links

This FGDC conformance check gets the last 100 bytes using an [HTTP Range request](https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests) to read the end-of-central-directory (EOCD) section in a target zip file. The EOCD section contains a complete file listing and file byte offsets in the ZIP.  File listings are then verified to have a geospatial extension.

## Recognized File Extensions
 - gpkg
 - shp
 - gdb
 - geojson
 - kmz
 - kml
 - gml
 - gpx
 - vct
 - tab
 - osm
 - dlg
 - img
 - asc
 - tif
 - rst
 - pix
 - ecw
 - jp2
 - sid
 - mdb
 - mbtiles
 - vmds
 - sqlite
 - las
 - laz
 - xyz
 - dem
 - hdf

>It is important to note that enabling the HTTP Range header is completely optional for caching data in Geoplatform. 

Besides enabling Range header on the server, some other reasons this rule may fail:

- No ZIP64 support
- No encrypted ZIP support
- No stream support
- Long comments in a ZIP file

### ISO 19115

*//gmd:transferOptions/gmd:MD_DigitalTransferOptions/gmd:onLine/gmd:CI_OnlineResource/gmd:linkage/gmd:URL/text()*

### ISO 19115-3

*//mrd:transferOptions/mrd:MD_DigitalTransferOptions/mrd:onLine/cit:CI_OnlineResource/cit:linkage/gco:CharacterString/text()*

### More Information

- [FGDC Technical Guidance: Data.gov and The GeoPlatform Metadata Recommendations](https://www.fgdc.gov/technical-guidance/metadata/fgdc-technical-guidance-datagov-geoplatform-ngda.pdf)
- [HTTP Range Header](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Range)
- [HTTP Range request](https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests)