A short history lesson on simple features

During the mid 1990s, interest in simple geometric structures grew. Disk storage and hardware costs in general decreased while computational speed increased. At the same time, existing geographic information system (GIS) datasets were more readily available, and the work of GIS users was evolving from primarily data compilation activities to include data use, analysis, and data sharing. "Interoperability" was a major buzzword.

Users wanted faster performance for data use (for example, deliver the feature coordinates of these 1,200 polygons as quickly as possible). Thousands of GISs were in use and numerous datasets were readily available.

Around this time, Esri developed and published its Esri Shapefile format. Shapefiles used a simple storage model for feature coordinates. Each shapefile represented a single feature class (of points, lines, or polygons) and used a simple storage model for the feature's coordinates. Shapefiles could be easily created from many GIS systems. Over time, shapefiles were widely adopted as a de facto standard and are still widely used and deployed today.

A few years later, ArcSDE pioneered a similar simple features storage model in relational database tables. A feature table could hold one feature per row with the geometry in one of its columns along with other feature attribute columns.

A sample feature table of state polygons is shown below. Each row represents a state and the columns hold the attribute properties for each. One of the columns (the shape column) holds the polygon geometry of each state.

This simple features model fit the structured query language (SQL) processing engine well. Through the use of relational databases, GIS data began to scale to unprecedented sizes and numbers of users without degrading performance. This was the start of leveraging relational database management systems (RDBMS) for GIS data management.

Shapefiles became ubiquitous and this simple features mechanism became the fundamental feature storage model across the GIS industry. (To support interoperability, Esri was the lead author of the Open Geospatial Consortium (OGC) and International Organization for Standardization (ISO) simple features specification).

Simple feature storage had clear advantages. These included the following:

• The complete geometry for each feature is held in one record. No assembly is required.
• The data structure (physical schema) is simple, fast, and scalable.
• It is easy for programmers to write interfaces.
• It is interoperable. Many people wrote simple converters to move data in and out of these simple geometries from numerous other formats. Shapefiles were widely applied as a data use and interchange format.

For more information on simple features, see Topology_basics.