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Shoreline Data

Providing shoreline data to the coastal community

Creating Historical Vector Shoreline Data

This section provides detailed technical information on the process of creating vector shoreline data. In addition, there are several manuals on the georeferencing and vectorization process, an error assessment paper on vector data derived from scanned T-Sheets, and a report on the methods behind the quality assurance/quality control (QA/QC) standard operating procedures that are used to check for line and attribute accuracy during production.

| Creating Shoreline Maps | Manuals and Reports |

Creating Historical Shoreline Maps

The NOAA Coastal Services Center has produced high-resolution vector shoreline data from scanned shoreline maps. The shoreline maps have been vectorized, or traced, and these vector data are made available from this site.

NOAA's coastal mapping is performed by the National Ocean Service's (NOS) National Geodetic Survey (NGS), whose primary mission is to survey the nation's coast and provide accurate positions of the shoreline. The creation of coastal survey maps and shoreline data begins with the collection of shoreline data from tide-controlled aerial photography using stereo photogrammetry. Shoreline data are measured using the programmetric process and recorded on shoreline maps. Historical shoreline maps have been assigned registry numbers with a "T" or "TP" identification series. Over the years, maps from these series have come to be referred to as NOS T-sheets. View a portion of a T-sheet by following this link.

Types of Software Used

All 13,000 archived shoreline maps have been scanned into a raster format. The software used to vectorize the shoreline raster files is called ArcScan, produced by Environmental Systems Research Institute, Inc. (ESRI®). ArcScan is an extension that operates within the ArcGIS® software environment. This program allows the user to automatically trace lines in a "heads-up" digitizing mode (digitizing on the computer screen with a mouse, as opposed to using a digitizing table). The software user also can clean linework errors and assign attributes to the data.

Before these raster files can be used in ArcScan, they must be converted into ARC GRID® format. Once the shoreline files are in a grid format, they are georeferenced to a specific projection and horizontal datum. This is done so that the resulting vector files will also be georeferenced. The user is then able to begin vectorizing the raster data, creating vector data in an ARC/INFO coverage format. Data in vector format are more useful in a geographic information system (GIS), are easily altered and updated, and require less storage space on a computer.

During the vectorization process, attention to linework accuracy and coding is assured through quality checks by a GIS analyst familiar with the process. Maps are created that illustrate the original T-sheet, the derived linework that was vectorized, and the assigned attribute codes for each line segment. By reviewing these maps on a light table, the analyst is able to determine errors that need correcting.

Once all T-sheets for a state have been vectorized, the individual files are joined together so that all lines are connected through a process known as edge matching. All files are appended together into a statewide file. Coordinates in the statewide files are in decimal degrees, referenced to the North American Datum of 1983 (NAD83). Documentation is written that explains to other users of the data the various methods that were followed to create the final coverage. The documentation, also known as metadata, is in a standard format developed by the Federal Geographic Data Committee (FGDC).

The Final Steps

The final step is to provide public access to the vector data.
Access historical vector data and metadata.

Manuals and Reports

Several documents may be useful in better understanding the processes used to create the vector shoreline data.

The manuals and reports are in Portable Document Format (PDF). Download Adobe® Acrobat Reader to view these files.

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