Department of Environmental Protection Pennsylvania DEP Locational Data Policy

Transcription

1 Department of Environmental Protection Pennsylvania DEP Locational Data Policy

2 COMMONWEALTH OF PENNSYLVANIA Department of Environmental Protection January 22, 2001 SUBJECT: FINAL TECHNICAL GUIDANCE TO: Technical Guidance Distribution List FROM: Nancie Imler Director Bureau of Program Integration and Effectiveness THROUGH: Kimberly Nelson Chief Information Officer Office of Information Technology THROUGH: Richard P. Mather Director Bureau of Regulatory Counsel DOCUMENT NUMBER: TITLE: LOCATIONAL DATA POLICY TYPE OF CHANGE TO TECHNICAL GUIDANCE MANUALS: Draft Guidance X - Final Guidance Substantive Revision LOCATION: Volume 1, Tab 12 CONTACT PERSON: Gail Jackson, Chief Division of Data Administration Bureau of Program Integration and Effectiveness 3rd Floor, Rachel Carson State Office Building 400 Market Street Harrisburg, PA Phone: (717) Fax: (717) gajackson@state.pa.us ( )

3 Subject: Locational Data Policy PURPOSE This policy establishes the standards and requirements for collecting and documenting latitude and longitude coordinates and elevation data for facilities, sites, monitoring points, observation points and other regulated entities or locations of interest under the jurisdiction of the Pennsylvania Department of Environmental Protection (DEP). The intent of this policy is to ensure the uniformity, reliability and compatibility of DEP s locational data, thereby promoting the enhanced use of DEP s extensive data resources for cross-media environmental analyses and management decisions. This policy underscores DEP s commitment to establishing the data infrastructure necessary to enable data sharing and secondary data use. DEFINITIONS This policy requires the clear understanding of those terms generally associated with locational information. A Glossary of relevant terms is attached. SCOPE AND APPLICABILITY This policy applies to all DEP organizations, delegated agencies, contractors, and grantees who design, develop, compile, collect, operate or maintain DEP information repositories developed for environmental program support. Certain requirements of this policy apply to existing as well as new data collections. BACKGROUND a. Fulfillment of DEP s mission to protect and improve the air, land and water of the Commonwealth depends upon improvements in data sharing across programs. All programs share a common need for data that contains reliable locational information. b. Accurate, standardized, locational information will provide a significant return on DEP s sizeable investment in environmental spatial data and ensure data availability for future applications not currently anticipated. c. Readily available, reliable, and consistent location identification data are critical to support DEP-wide development of environmental risk management strategies, methodologies, and assessments. d. The Office of Information Technology is committed to working with DEP programs to apply spatially related tools, e.g., GIS, remote sensing, mapping and imagery software to daily tasks. This office will also ensure these tools are supported with adequate and accurate location identification data. Effective use of spatial data depends on the appropriate collection and use of location identifiers and on the accompanying data and attributes to be analyzed. POLICY a. It is DEP policy that latitude/longitude coordinates along with accompanying method accuracy and description (MAD) information be collected and documented with environmental and related data. This is in addition to, and not precluding, other critical location identification data that may be needed to satisfy individual program or project needs, such as depth, street address, elevation or altitude.

4 b. This policy serves as a framework for collecting and documenting location identification data. Within 6 months of final adoption of this policy, DEP Program managers shall have in place program specific guidance for implementation of this policy. This guidance shall include information on the exact levels of precision and accuracy necessary to support their mission within the context of the goals of this policy. Collection of latitude and longitude information should be ongoing. Collection and input of the additional required locational data information shall begin as soon as the Department data system is prepared to accept and store this information. The department will also modify it s information collection forms, such as the General Information Form (GIF), to collect additional locational data information needed to support this policy when this information is provided from an outside source, such as a permit applicant or consultant. The ultimate goal is for a 10-meter/32.8 Feet or better level of accuracy. The use of global positioning systems (GPS) is recommended to obtain latitude/longitude of sufficient accuracy to meet program and department goals and to correctly locate the facility. Manual methods of obtaining latitude/longitude such as ups and overs, should be used only where absolutely necessary and should ultimately be eliminated as a method for obtaining locational data. The target date for cessation of manual methods such as ups and overs is January 1, For purposes of this policy, the use of the functionality that is available through the e-facts Spatial system is not considered a manual method and may continue to be used to satisfy the requirements of this policy. c. In Appendix A, attached to this policy, is a list of existing codes from the EPA Environmental Data Registry and descriptions for each of the datum types and codes. These lists are provided as an example of the type of information that may be appropriate. The final lists will be developed after adoption and before implementation of this policy and will include those values needed to support the accurate classification of information and data sharing for PADEP. d. To implement this policy, program managers must direct staff, to collect and document, at a minimum, the following required information. Latitude/Longitude and Accuracy Information 1. Latitude Measure The measure of the angular distance on a meridian north or south of the equator. 2. Longitude Measure The measure of the angular distance on a meridian east or west of the prime meridian 3. Horizontal Accuracy Measure The measure of the accuracy in feet of the latitude and longitude coordinates. The format for representing this information is: + DD MM SS.SSSS (latitude) - DDD MM SS.SSSS (longitude) Where: Latitude is always presented before longitude DD represents degrees of latitude; a two-digit decimal number ranging from 00 through 90 DDD represents degrees of longitude; a three-digit decimal number ranging from 000 through 180 MM represents minutes of latitude or longitude; a two-digit decimal number ranging from 00 through 60 SS.SSSS represents seconds of latitude or longitude, with a format allowing possible precision to the the-thousandths of seconds

5 + specifies latitudes north of the equator and longitudes east of the prime meridian - specifies latitudes south of the equator and longitudes west of the prime meridian Geometric Type 4. Code The code that represents the geometric entity represented by one point or a sequence of latitude and longitude points. 5. Name The description for the geometric type code. The final list will be developed after adoption and before implementation of this policy but it is anticipated that it will include such values as point, line, and area or polygon. This identifies the geometric entity that is represented by one set or more sets of latitude and longitude points. ). Horizontal Collection Method 6. Code The code that represents the method used to determine the latitude and longitude coordinates for a point on the earth. ). 7. Text The description for the horizontal collection method code that describes the method used to determine the latitude and longitude coordinates for the locational data being input.). The final list will be developed after adoption and before implementation of this policy but it is anticipated that it will include such values as method based on address matching to the house number, use of various GPS units, or unknown. Appendix A contains further examples of possible values. Horizontal Reference Datum 8. Code - The code that represents the reference datum used in determining latitude and longitude coordinates. 9. Name The name that describes the reference datum used in determining latitude and longitude coordinates. Reference Point 10. Code The code that represents the place for which geographic coordinates were established. 11. Text The description for the reference point code that describes the place for which geographic coordinates were established. The final list will be developed after adoption and before implementation of this policy but it is anticipated that it will include such values as front door, center of building, and plant entrance. 12. Source Map Scale Number - The number that represents the proportional distance on the ground for one unit of measure on the map or photo. Remarks: This is mandatory for all horizontal data collection methods except for methods using Global Positioning System (GPS). e. Additional location information may be collected as relevant. Examples include: Vertical Location Datum Altitude System Definition - The reference frame or system from which altitudes (elevations) are measured. The term "altitude" is used instead of the common term "elevation" to conform to the terminology in Federal Information Processing Standards.

6 Altitude Datum Name - The identification given to the surface taken as the surface of reference from which altitudes are measured. There are two available Datum: (1) The National Geodetic Vertical Datum of 1929 (NGVD29) and (2) The North American Vertical Datum of 1988 (NAVD88). At the time of this publication, the USGS DEM's use NGVD29 and this will cause any products using these DEM to reference NGVD29. Therefore until USGS adopts NAVD88, NGVD29 is the preferred Datum. It should be noted that NAVD88 had significant accuracy enhancements due to more advanced measuring techniques. Data, metadata, measurements taken and other accompanying documents referring to altitude/elevation data must make reference to the datum used. 1. Altitude (Vertical) Collection Method Code - The code that represents the method used to collect the vertical measure (i.e., the altitude) of a reference point. 2. Altitude (Vertical) Collection Method Text - The text that describes the method used to collect the vertical measure (i.e., the altitude) of a reference point. 3. Altitude Datum - The code representing the Altitude Datum used for calculation of the altitude. Data Collection Datum Data Collection Date - The calendar date when data were collected. RESPONSIBILITIES a. The Office of Information Technology shall: (1) Be responsible for implementing and supporting this policy. (2) Provide guidance and technical assistance where feasible and appropriate in implementing and improving the requirements of this policy. (3) The Bureau of Program Integration and Effectiveness will publish formats, standards, coding conventions or other specifications for the method, accuracy and description information. b. Deputy Secretaries, Bureau Directors, Regional Directors and program managers shall establish procedures within their respective organizations to ensure that information collection and reporting systems under their direction are in compliance with this policy. While the value of obtaining locational coordinates will vary according to individual program requirements, the method, accuracy and description of the coordinates must always be documented. Such documentation will permit other users to evaluate whether those coordinates can support secondary uses, thus addressing DEP data sharing and integration objectives. WAIVERS Requests for waivers from specified provisions of the policy may be submitted for review to the Executive Deputy Secretary for Policy and Communication. Waiver requests must be based clearly on data quality objectives and must be signed by the relevant Deputy Secretary prior to submission. This policy does not preclude or rescind more stringent regional or program-specific policy and guidance. Such guidance may require additional parameters such as elevation measurements to fully characterize the location of environmental observations.

7 APPENDIX A The following lists of codes are those codes related to the Locational Data Policy available for use in the Department of Environmental Protection s efacts system as of September 5, CODES for Locational Data Information Geometric Type AREA LINE POINT REGN ROUTE The area referenced by geographic coordinates. The line referenced by geographic coordinates. The point referenced by geographic coordinates. The geometric entity, described by locational coordinates, that includes two or more related areas is a region. The geometric entity, described by locational coordinates, that form a contiguous network is a route. Horizontal Collection Method AMBLF AMDIG AMHNO AMINT AMOTH AMPN AMSTC CB90 CB90G CB90T CENOT SURVY EFACT GPSKN GPSST GPSDF GPSPR GPSON GPSOF GPSCN GPS TIGER ITPMS The geographic coordinate determination method based on address matching-block face. The geographic coordinate determination method based on address matching-digitized. The geographic coordinate determination method based on address matching-house number. The geographic coordinate determination method based on address matching-nearest intersection The geographic coordinate determination method based on address matching-other. The geographic coordinate determination method based on address matching-primary name. The geographic coordinate determination method based on address matching-street centerline. The geographic coordinate determination method based on census block-1990-centroid. The geographic coordinate determination method based on census/group-1990-centroid. The geographic coordinate determination method based on census/tract-1990-centroid. The geographic coordinate determination method based on census-other. The geographic coordinate determination method based on classical surveying techniques. The geographic coordinate determination method based on efacts/efacts Spatial The geographic coordinate determination method based on GPS carrier phase kinematic relative positioning technique. The geographic coordinate determination method based on GPS carrier phase static relative positioning technique. The geographic coordinate determination method based on GPS code measurements (pseudo range) differential (DGPS). The geographic coordinate determination method based on GPS code measurements (pseudo range) precise positioning service. The geographic coordinate determination method based on GPS code measurements (pseudo range) standard positioning service (SA Off). The geographic coordinate determination method based on GPS code measurements (pseudo range) standard positioning service (SA On). GPS Code Measurements (pseudo range) Standard Positioning Service Corrected using Canadian Active Control System. Global Positioning Method, with unspecified parameters. The geographic coordinate determination method is based on a digital map source (TIGER). The geographic coordinate determination method is based on the use of a Multi-Spectral Scanner (MSS).

8 ITPMP The geographic coordinate determination method based on interpolation-map. ITPOT The geographic coordinate determination method based on interpolation-other. ITPPH The geographic coordinate determination method based on interpolation-photo. ITPSP The geographic coordinate determination method uses SPOT (Systeme Probatoire d Observation de la Terre), a French-owned satellite launched in ITPSA The geographic coordinate determination method based on interpolation-satellite. ITPTM The geographic coordinate determination method is based on the use of a Thematic Mapper. LORAN The geographic coordinate determination method based on Loran C. PLSES The geographic coordinate determination method is based on a public land survey, an eighth of a section. PLSFT The geographic coordinate determination method is based on a public land survey footing. PLSQS The geographic coordinate determination method based on public land survey quarter of a section. PLSSC The geographic coordinate determination method based on public land survey section. PLSSX The geographic coordinate determination method is based on a public land survey, a sixteenth of a section. UNK Unknown ZPCEN The geographic coordinate determination method based on zipcode-centroid. ZP2CN The center of an area defined by the 5-digit ZIP code and its 2-digit geographic segment extension. ZP4CN The center of an area defined by the 5-digit ZIP code and its 4-digit geographic segment extension. NAD27 North American Datum of 1927 NAD83 North American Datum of 1983 GEO84 World Geodetic System of 1984 Horizontal Reference Datum Reference Point ADBLD AIRMN AIRST AIRVT ATETU CNTER CTROD INPIP LGOON LWTU LODCT LODNG CORNE CORNW ENTFT ENTGN ENTPE CNTAM PUNIT PUCEN CORSE CORSW Administrative Building - A building where business, school, or governmental business affairs are managed. Air Monitoring Station - The station where air monitoring occurs. Air Release Stack - The stack where air releases occur. Air Release Vent - The vent where air releases occur. Atmospheric Emissions Treatment Unit - The unit where atmospheric emissions are treated. The center of the facility. The centroid for the area where the facility is. Intake Pipe - A pipe where fluid enters an enclosure. Lagoon or Settling Pond - A body of water at rest, where clarification takes place as sediment is deposited. Liquid Waste Treatment Unit - The unit where liquid waste is treated. Loading Area Centroid - The centroid for the loading area. Loading Facility - The facility where loading occurs. Northeast corner of the land parcel. Northwest corner of the land parcel. Plant Entrance (Freight) - The freight entrance to a plant. Plant Entrance (General) - The general entrance to a plant. Plant Entrance (Personnel) - The personnel entrance to a plant. Potential source of contamination to drinking water supply. Process Unit - The unit where processing occurs. Process Unit Area Centroid - The centroid for the area where the process unit is. Southeast corner of the land parcel. Southwest corner of the land parcel.

9 SWSTR SWTDU H2OSR H2OPR SPRNG STANK UNK H2OMS H2OPI H2OWL WELL WELPA WELOG Solid Waste Storage Area - The area where solid wastes are stored. Solid Waste Treatment/Disposal Unit - The unit where solid wastes are treated or disposed of. Source Water Area - The area that potentially supplies water to a drinking water intake. Source Water Protection Area - The drinking water source area where protective management action occur. Spring - A place where ground water flows naturally from a rock or the soil into the land surface or into a body of surface water. Storage Tank Unknown - The information is not known. Water Monitoring Station - The station where water monitoring occurs. Water Release Pipe - The pipe where water releases occur. Water Well - A shaft or dug hole, whose depth is greater than its diameter, sunk into the ground to a depth that allows the withdrawal of water from a water-yielding geologic unit. Well - A pit or hole sunk into the earth to reach a supply of water. Wellhead Protection Area - The surface and subsurface area surrounding a water well or well field, supplying a public water system, through which contaminants are reasonably likely to move toward and reach such water well or well field. Oil or gas well Altitude (Vertical) Location Datum Collection Method Code ALTIM SRVEY GPSKN GPSST GPSDF GPSPR GPSOF GPSON LVLNB UNSPF PHGRM LVLBM TOPO TRGLV A method used to determine vertical components based on altimetry. Geographic coordinate determination method based on classical surveying techniques. Geographic coordinate determination method based on GPS carrier phase kinematic relative positioning technique. Geographic coordinate determination method based on GPS carrier phase static relative positioning technique. Geographic coordinate determination method based on GPS code measurements (pseudo range) differential (DGPS). Geographic coordinate determination method based on GPS code measurements (pseudo range) precise positioning service. Geographic coordinate determination method based on GPS code measurements (pseudo range) standard positioning service (SA Off). Geographic coordinate determination method based on GPS code measurements (pseudo range) standard positioning service (SA On). Leveling between non-benchmark control points. Other, unspecified. Photogrammetric. Precise leveling from a bench mark. Topographic map interpolation. Trigonometric leveling. Altitude Datum Code and Description Code Description NGV29 National Geodetic Vertical Datum of 1929 NAV88 North American Vertical Datum of 1988

10 APPENDIX B LOCATIONAL POLICY GLOSSARY Attribute A characteristic of a geographic feature described by numbers, characters, images and CAD drawings, typically stored in tabular format and linked to the feature by a userassigned identifier (e.g., the attributes of a well might include depth and gallons per minute). A column in a database table. Attribute table An INFO or other tabular file containing rows and columns. In ArcInfo, attribute tables are associated with a class of geographic features, such as wells or roads. Each row represents a geographic feature. Each column represents one attribute of a feature, with the same column representing the same attribute in each row. COGO Abbreviation of the term COordinate GeOmetry. Land surveyors use COGO functions to enter survey data, to calculate precise locations and boundaries, to define curves, and so on. The name of the ArcInfo coordinate geometry software product. Contiguity The topological identification of adjacent polygons by recording the left and right polygons of each arc. Continuous data A surface for which each location has a specified or derivable value. Typically represented by a tin or lattice (e.g., surface elevation). Contour A line connecting points of equal surface value. Contour interval The difference in surface values between contours. Coordinate A set of numbers that designate location in a given reference system, such as x,y in a planar coordinate system or an x,y,z in a three-dimensional coordinate system. Coordinates represent locations on the Earth's surface relative to other locations. Coordinate system A reference system used to measure horizontal and vertical distances on a planimetric map. A coordinate system is usually defined by a map projection, a spheroid of reference, a datum, one or more standard parallels, a central meridian, and possible shifts in the x- and y-directions to locate x,y positions of point, line, and area features. In ArcInfo, a

11 system with units and characteristics defined by a map projection. A common coordinate system is used to spatially register geographic data for the same area. Coverage A digital version of a map forming the basic unit of vector data storage in ArcInfo. A coverage stores geographic features as primary features (such as arcs, nodes, polygons, and label points) and secondary features (such as tics, map extent, links, and annotation). Associated feature attribute tables describe and store attributes of the geographic features. A set of thematically associated data considered as a unit. A coverage usually represents a single theme such as soils, streams, roads, or land use. Coverage units The units (e.g., feet, meters, inches) of the coordinate system in which a coverage is stored. Datum A set of parameters and control points used to accurately define the three-dimensional shape of the Earth (e.g., as a spheroid). The datum is the basis for a planar coordinate system. For example, the North American Datum for 1983 (NAD83) is the datum for map projections and coordinates within the United States and throughout North America. Digital elevation model A digital representation of a continuous variable over a two- dimensional surface by a regular array of z values referenced to a common datum. Digital elevation models are typically used to represent terrain relief. Also referred to as 'digital terrain model' (DTM). An elevation database for elevation data by map sheet from the National Mapping Division of the U.S. Geological Survey (USGS). The format of the USGS digital elevation data sets. Double Precision Refers to a high level of coordinate accuracy based on the possible number of significant digits that can be stored for each coordinate. ArcInfo data sets can be stored in either single- or double-precision coordinates. Double-precision coverages store up to 15 significant digits per coordinate (typically, 13 to 14 significant digits), retaining the accuracy of much less than one meter at a global extent. Format The pattern into which data are systematically arranged for use on a computer. A file format is the specific design of how information is organized in the file. For example, ArcInfo has specific, proprietary formats used to store coverages. DLG, DEM, and TIGER are geographic data sets with different file formats. Geocode The process of identifying the coordinates of a location given its address. For example, an address can be matched against a TIGER street network to determine the location of a home. Also referred to as address geocoding.

12 Geographic data The locations and descriptions of geographic features. The composite of spatial data and descriptive data. Geographic database A collection of spatial data and related descriptive data organized for efficient storage and retrieval by many users. Geographic data set One of seven geographic data types supported by ArcInfo. Geographic data sets in ArcInfo include coverages, grids, DBMS tables, tins, images, lattices, and CAD drawings. Geographic feature A user-defined geographic phenomenon that can be modeled or represented using geographic data sets in ArcInfo. Examples of geographic features include streets, sewer lines, manhole covers, accidents, lot lines, and parcels. Georeference To establish the relationship between page coordinates on a planar map and known realworld coordinates. Image A graphic representation or description of a scene, typically produced by an optical or electronic device. Common examples include remotely sensed data (e.g., satellite data), scanned data, and photographs. An image is stored as a raster data set of binary or integer values that represent the intensity of reflected light, heat, or other range of values on the electromagnetic spectrum. Latitude-Longitude A spherical reference system used to measure locations on the Earth's surface. Latitude and longitude are angles measured from the Earth's center to locations on the Earth's surface. Latitude measures angles in a north-south direction. Longitude measures angles in the east-west direction. Lattice A surface representation that uses a rectangular array of mesh points spaced at a constant sampling interval in the x and y directions relative to a common origin. A lattice is stored as a grid, but represents the value of the surface only at the mesh points rather than the value of the entire cell. Layer A thematic set of spatial data described and stored in an ArcStorm database or a LIBRARIAN map library. Layers organize a database or map library by subject matter

13 (e.g., soils, roads, and wells). Conceptually, layers in a database or map library environment are exactly like coverages. Map projection A mathematical model that transforms the locations of features on the Earth's surface to locations on a two-dimensional surface. Because the Earth is three-dimensional, some method must be used to depict a map in two dimensions. Some projections preserve shape; others preserve accuracy of area, distance, or direction. Map projections project the Earth's surface onto a flat plane. However, any such representation distorts some parameter of the Earth's surface be it distance, area, shape, or direction. Map scale The reduction needed to display a representation of the Earth's surface on a map. A statement of a measure on the map and the equivalent measure on the Earth's surface, often expressed as a representative fraction of distance, such as 1:24,000 (one unit of distance on the map represents 24,000 of the same units of distance on the Earth). Map scale can also be expressed as a statement of equivalence using different units; for example, 1 inch = 1 mile or 1 inch = 2,000 feet. Map units The coordinate units in which a geographic data set (e.g., a coverage) is stored in ArcInfo. Map units can be inches, centimeters, feet, meters, or decimal degrees. A line running vertically from the North Pole to the South Pole along which all locations have the same longitude. The Prime Meridian (0) runs through Greenwich, England. From the Prime Meridian, measures of longitude are negative to the west and positive to the east up to 180, halfway around the globe. Mesh Point One sample point in the array of sample points in a lattice. Each mesh point is located at a constant sampling interval in the x and y directions relative to a common origin, and contains the z value for the surface at that location. Mesh points outside the surface, or which represent holes in the surface, are assigned a null value. Metadata Metadata describe the content, quality, condition and other characteristics of data. Metadata help a person locate and understand data. Metadata include information needed to determine the sets of data that exist for a geographic location, information needed to determine if a set of data meets a specific need, information needed to acquire an identified set of data and information needed to process and use a set of data. The exact order in which data elements are evaluated, and the relative importance of data elements, will not be the same for all users. Minimum mapping units For a given map scale, the size or dimension below which a long narrow feature is represented as a line and a small area as a point. For example, streams and rivers will be

14 represented as lines if their width is less than.10 inch, and polygons smaller than.125 inch on a side will be represented as a point. Point A single x,y coordinate that represents a geographic feature too small to be displayed as a line or area; for example, the location of a mountain peak or a building location on a small-scale map. A coverage feature class used to represent point features or to identify polygons. It is not possible to have point and polygon features in the same coverage. When representing point features, the x,y location of the label point describes the location of the feature. When identifying polygons, the label point can be located anywhere within the polygon. Attributes for points are stored in a PAT. Point-in-polygon A topological overlay procedure which determines the spatial coincidence of points and polygons. Points are assigned the attributes of the polygons within which they fall. Polygon A coverage feature class used to represent areas. A polygon is defined by the arcs that make up its boundary and a point inside its boundary for identification. Polygons have attributes (PAT) that describe the geographic feature they represent. Polygon-arc topology The topological data structure ArcInfo uses to represent connectivity between arcs to form polygons. Polygon-arc topology supports the definition of polygons and analysis functions such as topological overlay. Polygon overlay A topological overlay procedure which determines the spatial coincidence of two sets of polygon features and creates a new set of polygons based on identity, intersect, or union. Projection file A coverage file that stores the parameters for the map projection and coordinate system of a geographic data set (e.g., a coverage). A text file containing input and output projection parameters that can be used to convert a geographic data file from one coordinate system to another. Proximal tolerance The minimum distance in ground units separating all point locations on the horizontal plane. If two or more points are found within the proximal tolerance distance of each other, only the first point read is passed for further processing Raster A cellular data structure composed of rows and columns for storing images. Groups of cells with the same value represent features.

15 Rectification The process by which an image or grid is converted from image coordinates to real-world coordinates. Rectification typically involves rotation and scaling of grid cells, and thus requires resampling of values. Remote sensing Acquiring information about an object without contacting it physically. Methods include aerial photography, radar, and satellite imaging. Resolution Resolution is the accuracy at which a given map scale can depict the location and shape of geographic features. The larger the map scale, the higher the possible resolution. As map scale decreases, resolution diminishes and feature boundaries must be smoothed, simplified, or not shown at all. For example, small areas may have to be represented as points. Distance between sample points in a lattice. Size of the smallest feature that can be represented in a surface. The number of points in x and y in a grid or lattice (e.g., the resolution of a U.S. Geological Survey one-degree DEM is 1201 x 1201 mesh points). Spatial data Information about the location and shape of, and relationships among, geographic features, usually stored as coordinates and topology. TIGER The Topologically Integrated Geographic Encoding and Referencing data format used by the U.S. Census Bureau to support census programs and surveys. It was used for the 1990 census. TIGER files contain street address ranges along lines and census tract/block boundaries. This descriptive data can be used to associate address information and census/demographic data with coverage features. TIN (Triangulated irregular network) This is an ArcInfo product used for surface representation, modeling and display. A surface representation derived from irregularly spaced sample points and breakline features. The tin data set includes topological relationships between points and their neighboring triangles. Each sample point has an x,y coordinate and a surface, or z-value. These points are connected by edges to form a set of non-overlapping triangles used to represent the surface. Tins are also called irregular triangular mesh or irregular triangular surface model. Topographic map A map containing contours indicating lines of equal surface elevation (relief), often referred to as topo maps. Often used to refer to a map sheet published by the U.S. Geological Survey in the 7.5- minute quadrangle series or the 15-minute quadrangle series.

16 Topological overlay An analysis procedure for determining the spatial coincidence of geographic features. ArcInfo supports overlay among and between all feature classes. Topology The spatial relationships between connecting or adjacent coverage features (e.g., arcs, nodes, polygons, and points). For example, the topology of an arc includes its from- and to-nodes, and its left and right polygons. Topological relationships are built from simple elements into complex elements: points (simplest elements), arcs (sets of connected points), areas (sets of connected arcs), and routes (sets of sections, which are arcs or portions of arcs). Redundant data (coordinates) are eliminated because an arc may represent a linear feature, part of the boundary of an area feature, or both. Topology is useful in GIS because many spatial modeling operations don't require coordinates, only topological information. For example, to find an optimal path between two points requires a list of the arcs that connect to each other and the cost to traverse each arc in each direction. Coordinates are only needed for drawing the path after it is calculated. USGS DEM A digital elevation model produced by the Survey Branch of the United States Department of the Interior, consisting of a regular array of elevations referenced in the Universal Transverse Mercator (UTM) coordinate system. These data correspond to the standard 1:24,000-scale 7.5 x 7.5-minute quadrangles or 1:250,000 one-degree map sheets. Elevations are in meters or feet referenced to mean sea level. Vector A coordinate-based data structure commonly used to represent linear geographic features. Each linear feature is represented as an ordered list of vertices. Traditional vector data structures include double-digitized polygons and arc-node models.