Author: Debra Dinville

Title: Serving Reference Data

The Bureau of Land Management (BLM) is developing a Reference Theme Serving System (RTSS) to provide spatial reference data to BLM offices to support the overall Bureau mission of managing public lands. This system will be integrated into the current BLM GIS software to provide an efficient means to manage and distribute basic spatial information within BLM. This paper discusses some of the key issues and current approaches under consideration for implementing the RTSS.

The Bureau of Land Management (BLM) needs maps and imagery that accurately show the location of its land records, resource data, and for use in GIS analysis. BLM�s data needs to be displayed with familiar landmarks such as roads, waterways, topography, or administrative boundaries. BLM requires several types of background features called "reference themes," which can be displayed with BLM�s data.

Within BLM the reference themes are considered fundamental to a variety of program work. For example, archeologists, cultural resource consultants and the Forest Service working with BLM need the site locations and survey area themes compiled to be oriented with base geographic data to create meaningful representations, for improved accuracy of cultural data, and for analysis. State Historic Preservation Officers are mandated by Congress to maintain records, and through a National Program Agreement with BLM, use this data in conjunction with GIS applications. Reference data was identified as essential in conjunction with other resource, and field-collected data such as Global Positioning System (GPS) information. Reference themes would be queried for aesthetic view impact, wildlife habitat, or cultural impact for a proposed land action. In general, most resource specialists emphasized the need for base spatial data, easily accessible for specific projects.

BLM distributes data and information through Information Access Centers, formerly called Public Rooms. Access to reference themes, in conjunction with other resource data, could be printed on-demand in the Centers and a general user interface will be designed. This will allow the public to select the area of interest and pay for one map over the desired area they plan to visit. As this information is made available over the Internet, customers will no longer have to travel, but instant customer service and convenience will be addressed.

The BLM Land and Resource Information Systems Program Office in Denver intends to make geospatial data available to staff through Reference Theme Serving System (RTSS). This project will provide reference data, restructured into an easily usable format, and provide efficient access to reference data throughout the BLM for managers, resource specialists and Information Access Centers. This system will provide efficient, automatic distribution of data vs. personal interaction for locating, formatting and serving data. The data will be readily accessible for various BLM programs such as Cultural Resources, Fire, Wildlife, Minerals, Cadastral and Permit Renewal programs as well as utilized in Environmental Assessments. Direct support to the overall Bureau mission of managing the public lands will be provided in this system.

The RTSS is a new idea in delivering map and image data to the desktop. To develop this capability will require technical solutions for serving large volume, seamless data for Bureau distribution. The use of these reference themes is broad in scope: for use by managers for orientation concerning actions on the land, by resource specialists to address program areas, to support non-surveyed boundary information, and in GIS analysis. This project will involve development of the data sets to appear seamless and application of compression techniques to serve the data within response parameters, perfect the serving architecture, write appropriate user interface, and deploy the hardware needed. The RTSS will allow BLM to have consistent spatial data, have easy access to current spatial data, operate more efficiently, and make better business decisions. As everything relates to the land, having reference themes readily available for use, is a logical part of doing Bureau business.

The RTSS as envisioned must:

� include both image and map data, in at least two scales of each;

� provide 100% coverage of BLM interest areas and be orthogonally rectified to a uniform projection and datum;

� be served quickly and in a uniform manner at all Bureau locations; and

� incorporate new or emerging technology in the serving strategy.

The BLM is seeking to provide reference themes of several general types. The data selected for use is public domain from the U.S. Geological Survey. The identified data sets need to be restructured to appear seamless, tailored to best interact with the RTSS and processed to be able to be used as reference information with other resource data.

The scanned 1:24,000 quadrangle map data, or Digital Raster Graphic (DRG) was selected, as it will initially be the most comprehensive source for 100% coverage in the western states where the BLM has major land management responsibilities. The DRG single band 4-bit TIFF image will need to be tailored to best interact with the RTSS. The database must also be structured to facilitate accuracy and responsiveness. One requirement for the DRG data is that the data be pre-processed to remove the collar, as a seamless coverage. Removing the collar, and thus the metadata for the DRG, will require addressing the Federal Geographic Data Committee's metadata requirements by a link to a state index grid.

Vector map data, as provided by USGS in the 1:100,000 scaled Digital Line Graphs (DLG) over the Internet, was also selected. BLM plans to use this free source of data to serve as general reference elements, as well. Display of simple line-work, however, is not the intent. The data will be reprocessed to automatically show cartographic symbology when viewed. The original Spatial Data Transfer Standard formatted data will be converted to a format that facilitates the addition of attribute fields that will be used by ArcView to produce a unique classification legend. An AML program written by the BLM has been modified in a prototype with Esri to construct such attributes in the feature attribute tables of the data layers.

Thematic Mapper imagery, from the Multiple Regional Land Cover (MRLC) 30-meter database will be used, and compression and format issues will be addressed. Contiguous 30-meter coverage will be obtained through the USGS EROS Data Center. Issues concerning the original TM data, which is composed of 6 bands, 8-bit TIFF files and use of compression techniques needs to be further refined. More detailed imagery from the USGS Digital Orthophoto Quadrangle program will also be addressed by RTSS. Due to the definition and resolution associated with more detailed imagery, implementation of this data will be determined as it becomes available.

Large, raster databases of elevation data are being developed by the USGS EROS Data Center. One such data set, the National Elevation Database (NED), will be used to build hillshade (or shaded relief) files as a reference them. NED data sets which are primarily based on 30-meter data, resampled to one arc second, will be acquired for contiguous BLM coverage. EROS has processed NED data for BLM in New Mexico, and there are plans in place to complete coverage for the BLM administered western states. BLM is also looking at serving Digital Elevation Models (DEM) for more analytical work.

The RTSS project will help address storage, serve a format easily utilized, and provide efficiency of access to reference data. The RTSS is seen as being as simple as a button in ArcView which will allow a variety of users access to the desired reference theme for their particular application. In this project, distribution of this data over the Internet will also be evaluated and a user interface will be developed for general access.

The concept of reference themes requires developing massive, seamless databases that are fully geo-referenced. That means that the user can access the reference theme information with a request for data on a specific area of interest. The database server will quickly respond with reference theme data that has been clipped and registered to the same window as the other displayed data. The technical requirements to geo-reference, store, and serve this data are challenging, especially since most data will be in raster format, and will have to be transmitted to the user console with each window update. In serving the data there are a number of issues, which need to be addressed: compression, architecture, and database maintenance.

One technique to limit the amount of data to be transferred is to send only that data needed to fill the client�s window. Most data serving strategies break an image into small sections, called "tiles." The size of a tile can vary greatly depending on the design of the database. When a user requests data to cover their interest area, those tiles that fall entirely or in part, within the window, are sent to the client�s computer. Because the user�s window will never exactly match the tile grid, excess data is set to the client�s computer. To avoid sending more data than is needed, there are newer techniques that give a location address to each of the smallest picture elements (or pixels) of the raster, so that only the data that is within the user�s window is transmitted.

Another technique is a multi-resolution display. This approach assumes that the display will always be on a computer screen, and that there is no need to transmit more data than the screen can effectively display. Therefore, when the user views a large area in the window, one that encompasses a great amount of territory, the serving software automatically resamples the data so that only what can be effectively displayed is transmitted.

A final step to minimize the amount of data transmitted is data compression. Recent advances in compression technology have produced "compression engines" that can shrink typical image files up to 1/100th the size of the original. There is a "cost" to using this technology, in that there is some loss in fidelity compared to the original image, and that the computer must work to compress and decompress the data. However, these are acceptable costs given the great reduction in data transmitted.

Working with large data sets requires compression of data at the server side, and decompression at the client side. An initial evaluation of compression techniques has been completed, looking at both public domain and commercial sources. BLM completed a technology review based on the requirement to maximize use of existing Commercial Off-the Shelf software (COTS) and the ability to integrate the application with current ArcView applications. After initial elimination of image formats, only Multi-resolution Seamless Image Database (MrSID) and Joint Photographic Experts Group (JPEP) File Interchange Format (JFIF) are formats under consideration. MrSID, by Lizard Tech Inc., is a wavelet based imaging technology that compresses raster images of any size with little or no degradation in image quality. JPEG is commonly thought of as an image format, however, JPEG is actually a compression format, not a file format, using a 24-bit compression technique for storing full color and gray scale images.

The importance of database management and distribution is central to the development of the RTSS. Initial calculation for the datasets described indicate a total storage requirement of 2031.19 Gb. The following table identifies the requirements by State and data type:

The total size requirements are based on the generation of seamless quadrangle boundary layers for each of the data types. The reference theme sample data, compression analysis was used as an average quadrangle size for each data type.

Elements of the Bureau architecture that are required for the RTSS, include the need to interface with the existing BLM database management system, Informix. The data and user requirements of the RTSS require the ability to quickly retrieve data from database management systems. The datasets to be managed and served through the RTSS require system scalability and support access by many users, through a variety of communication methods. The hardware needed for distribution, storage and data access across local and wide area networks and the Internet will need to be addressed. BLM is currently evaluating the communication capabilities and requirements for the RTSS and the results will be used to define system design.

The RTSS is a recent project designed to help facilitate Bureau business and GIS analysis. The value of working with reference themes, readily accessible on a user's desktop is seen as beneficial to the day-to-day business operations of BLM. Extensive use of reference theme data is seen with conventional GIS and for direct "map-on-demand" functionality. As the BLM embraces the concept of a corporate GIS, there may be an additional need for reference themes, or derivative products. Derivative products could be defined to explore potential combinations of data to address specific applications vs. general use. RTSS currently is focusing on the reference data and reprocessing of that data. The project will then move into the design phase, then development and plans to deploy the system incrementally with completion in 2002. BLM has taken the initial steps to serve general use reference data, has discussed the concept with several agencies and welcomes opportunities for partnerships.

Debra Dinville

Program Analyst, Spatial Coordination

Bureau of Land Management

P.O Box 25047

Bldg. 40, WO-510D

Denver, Co 80225

(303) 236-6430 (Phone)

(303) 236-1981 (FAX)