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If you are a surveyor in the United States, chances are you have visited the National Geodetic Survey (NGS) data sheet web page (www.ngs.noaa.gov/cgi-bin/datasheet.prl). The NGS Data Sheet is a document which provides positional coordinates and other geodetic information for survey stations which are part of the National Spatial Reference System (NSRS).
First published in the early 1990’s, the original NGS Data Sheet was an actual paper sheet with printed geodetic control information for a station. Surveyors would call the NGS Information Branch to request data sheets for all NGS geodetic control stations which were located within an area of a specified USGS topographic map.
The paper data sheet was replaced by a digital data sheet in 1994. A digital data sheet (Figure 1) contains field identifiers to make the data more accessible to computer programs, but allows for easy viewing with a simple text editor.
The media by which digital data sheets have been delivered has steadily progressed over the years, with the cost of delivery varying greatly. The purchase price of a data sheet is based on the cost incurred by NGS to retrieve, package, and mail out the data. In 1994 when NG S first introduced digital data sheets on CD-ROM, you could purchase several states for $50. A year earlier, you would pay $30 for just one county on floppy disk.
After NGS conducted a new cost analysis in 2003, the price of the data sheets on CD-ROM increased to $285. In order to maintain a "best value" product for the taxpayer, NGS decided to discontinue the data sheet on CD-ROM and move all CD-ROM data to the Web where it would be available at no cost to the public.
Today, on average, over 200,000 data sheets are retrieved per month by the general public from the NGS Data Sheet Web Page; all data previously supplied on CDROM is now available for free from the ARCHIVED section of this website.
The NGS Data Sheet Web Page is a simple design consisting of six retrieval buttons and six associated informational links (Figure 2).
Data Sheets come in two formats, the Standard ASCII format available from the DATASHEETS button; and the Spatial Data Transfer Standard (SDTS) format available from the SDTS button. The ASCII version is readable from your browser. The SDTS version is used for importing coordinates and related information into GIS software packages.
Clicking on the DATASHEETS button from the Web will provide you with a list of several retrieval methods (Figure 3). All retrievals will result in the display of a "station list" (Figure 4), from which you may choose one or more stations to obtain the corresponding data sheets. Simply click the station you want, then click the Get Datasheets button.
These retrieval methods query the NGS database directly. This means that you are receiving the most current information (NGS loads 4-5 new survey projects into the database every day). Unfortunately, some restrictions, such as size of retrievable area, must be enforced to prevent the database system from being overwhelmed. For those users who do not need the most up-to-date information and would rather obtain large datasets more quickly, the ARCHIVED DATASHEETS button provides a link to static files of data sheets retrieved at an earlier date. These data sheets are retrieved on a yearly basis and archived into county datasets. NGS also provides static files of data sheets for all stations loaded or changed within any given month. After downloading the yearly data sheet files, a user can keep them relatively up-to-date by downloading the monthly updates and merging the two files on their PC. Program DSUPDATE provides the mechanism for merging these files. Other software for use with data sheets include DSWIN for viewing, searching and extracting data sheets on your PC, and DSFILES for combining and splitting data sheet files. Both DSWIN and DSFILE have the capability of reformatting your data sheets into a delimited, single record format which some users require for loading databases, spreadsheets, or GIS packages. All programs are available from the `Tell me more’ section of the Data Sheet Web Page.
The NGS Data Sheet Web Page has steadily evolved over the years. It first debuted in 1996 as a simple page for entering a station ID to retrieve a single data sheet. As a result of continuous feedback from the user community, new features have been added to make information more accessible and less costly for the taxpayer. One of the more significant features added was the `Map Search’ retrieval method, which displays the `NGS Survey Control Map’ on which survey stations are overlaid (Figure 5). A standard station list accompanies the plotted points; data sheets are available from this feature via the `Get Datasheets’ button. The `NGS Survey Control Map’ is included in the federal government’s geodata website (www.geodata.gov) under the "Locations and Geodetic Networks" category. The geodata.gov site is part of the Geospatial One-Stop initiative, which is one of 24 Office of Management and Budget (OMB) Electronic-Government initiatives for enhancing government efficiency.
Other features of the NGS Data Sheet Web Page include a graphical display of various datum heights above mean lower low water (MLLW) for those NGS survey marks which were observed by NOAA’s Center for Operational and Oceanographic Products and Services for recording tide levels; and a link for submitting mark recovery information for any station in the NGS database.
The NGS Data Sheet Web Page is an integral part of the NGS Website (www.ngs.noaa.gov), which provides on-line access to various types of geodetic data in support of the nation’s transportation and communication infrastructure. For more information about NGS programs visit www.ngs.noaa.gov/INFO/What WeDo.html
Craig Larrimore is an Information Technology Specialist with the Systems Development Division of the National Geodetic Survey. He has been developing software applications for users of NGS data for more than 15 years.
A 1.351Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE