DC GIS harnesses the functionality of ArcGIS, such as topology, cartographic representation and versioning. It is critical to preserve the integrity and consistency of these rules and settings. Therefore, all data transactions use ArcSDE on the geodatabase. Agencies responsible for data maintenance need to utilize this standard for all data activities. GIS files shared among agencies must be in a geodatabase or in ArcSDE export format. Shapefiles are not to be used, except for public data distribution. Shapefiles may also be used for some minor interagency file sharing, except where the layers employ topology.
Layers published in the DC GIS database follow a naming convention denoting their theme and geography type, sometimes including a year where needed (“<Name or abbreviated name><geography type abbreviation>”). The geography type is “Pt” for point, “Ln” for line, an“Ply” for “polygon.” The following details this convention for Public Schools:
- Point Layer: PubSchPt
- Polygon Layer: PubSchPly
- Line Layer: PubSchLn
For a layer that has data for a particular year, such as census tracts. The format is “<Name or abbreviated name><last two digits of the vintage year><geography type abbreviation>.” For 2000 Census Tracts, that would be “Tract00Ply.” Feature dataset names do not exceed 25 characters in length.
For most datasets, a common set of items exists to name, locate, link, and ID each record. These items are:
- GIS_ID (String, 16) – This item contains the primary DC GIS key for the dataset. GIS IDs are implemented as a standard for capturing and managing features. Each feature that is created or updated by staff automatically have a unique GIS ID associated with it. Automated programs and checks ensure the assignment and uniqueness of these ids.
- NAME (String, 60) – This item contains the primary or common name of the feature.
- AID (Integer) (if appropriate) – A foreign key to the Master Address Repository
- WEB_URL (String, 125) (if appropriate) – This item holds the web link related to the site. In most cases, this contains a link to the web site of the organization the feature represents. It can also be an appropriate “dc.gov” link where available. Otherwise, it is an indirect url to a web site describing the feature, such as a non-profit organization. Commercial urls are avoided (i.e. McDonalds, Starbucks, etc.).
- Feature updated date – A time stamp recorded at the time a change was made to an individual feature.
A layer may not require all of these items, but the analyst reviews these specifications in designing the attribute table. Each layer has a GIS_ID. Column names do not exceed 25 characters in length. Hyphens and spaces are not allowed. Instead, underscores are used to separate column words. Column names are all uppercase.
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