Louisiana Administrative Code › Title 43 - NATURAL RESOURCES › Part XXVII - State Lands › Subpart 1 - Land Information Mapping and Map Records System › Chapter 13 - Digital Mapping Requirements › Section XXVII-1303 - Data Definitions

Current through Register Vol. 50, No. 6, June 20, 2024
A. The
				  following definitions of digital map data are presented to clarify their usage
				  and meaning under these standards.
1. Layer. A
				  layer can be either a complete digital map or any single component overlay for
				  a map. Layers may contain one or more components. A planimetric map, a
				  topographic map overlay, and a parcel map overlay would each be considered an
				  aggregated map layer consisting of various layer categories, with each category
				  consisting of designated component layers to allow for inclusion or deletion of
				  specific feature elements. Sections 1309-1313, Appendices A, B, and C include a
				  general listing of layer categories and feature elements to be included within
				  the digital database framework for all planimetric, topographic and parcel maps
				  to be developed under these standards.
2. Component. A component is a discrete type
				  of feature element that, in combination with other feature elements, creates a
				  layer. Examples of feature elements include highway route numbers, contour
				  lines, parcel identification numbers, and map grid lines. Each feature element
				  is composed of objects that graphically represent a component's extent (lines,
				  configuration or area) or that present information (symbols or text).
3. Objects. Objects are the base graphic
				  elements that represent map features. They are interrelated in a topological
				  data structure that defines the relationship of the elements to one another.
				  The primary objects used to create components are points, nodes, lines, and
				  areas. Because geographic spatial data handling is still a relatively new
				  science, a number of different terms have been used in the past to report these
				  objects. The terminology used here draws on the current working documents from
				  the National Committee for Digital Cartographic Data Standards. To facilitate
				  understanding, the object definitions presented herein are simplifications of
				  that framework (see §1315 A, Appendix D, Figure 1).
a. Points. Points are used to represent the
				  location of objects. In some cases, these are feature points or objects that
				  can be identified on the surface of the earth (e.g., manhole covers,
				  pretargeted benchmarks, etc.). In other cases, they are arbitrarily placed
				  label points (e.g., locations for the placement of text, symbology, etc.). In
				  still other cases, they are attribute points for areas or lines (e.g., parcel
				  dimensions, parcel identification numbers, etc.). The locations of attribute
				  points may or may not have to be calculated.
b. Nodes. Nodes represent the intersection of
				  lines (linear objects). Each node must represent the intersection or
				  beginning/ending point of at least one line as a minimum. A node should
				  reference each line that intersects it and whether it is the beginning or
				  ending point of that line.
c.
				  Lines. Lines are strings of coordinates that run between nodes. Each line has a
				  minimum of two X and Y Louisiana State Plane Coordinate pairs. Beginning and
				  ending node numbers and identifiers of areas (when applicable) on the right and
				  left of the line will also be associated with each line.
d. Areas. Areas are polygons, which are
				  defined by a series of lines. Areas also include references to attribute points
				  and other associated data. The boundary of an area is defined by a listing of
				  the lines that comprise the area's border. The number of areas and a list of
				  lines composing each area are also recorded.
4. Topological Data Structure. Topology is
				  the mathematical relationship of how points and lines on a map interact with
				  one another to define geographic areas. The use of a topological data structure
				  is essential for the effective creation and manipulation of geographic data.
				  Topology allows the interrelationships of graphic objects to be specified. It
				  also prevents the storage of repetitive data. Thus, one line can represent a
				  stream and the boundary of two adjacent areas or parcels. This structure allows
				  the generation of areas based on node and line information. Topological
				  structures are necessary if analysis of lines or areas is undertaken. Thus,
				  road networks stored in a format with topological structure can be used for
				  data aggregation, maintenance inventories, school bus routing, or emergency
				  service dispatching.
5. Digital
				  Data Sets. Digital data sets are computer files that store geographic files
				  that store geographic data. Each data set may contain a number of components.
				  For example, a data set containing contour line components would also contain
				  contour labels. A street and roads data set could include pavement extent,
				  pavement and base course thickness, average daily traffic volume, right-of-way
				  limits, route labels, and related information.
6. Digital Labeling. Important differences
				  exist between the attribute points of lines and areas as opposed to label
				  points. Attribute points and associated information are stored or linked to
				  each line, area, or feature point. They allow users to select the specific
				  objects that they wish to plot, report on, or analyze. Thus, all of the line
				  segments that constitute Louisiana Highway No. 30 could be extracted and
				  plotted. Label points are used to label an object or a series of objects on a
				  map. Thus, two different label points may be used to identify Highway No. 30 as
				  it crosses a map, where 13 lines, each with an associated attribute point, are
				  used to plot Louisiana Highway No. 30 on the map (see §1315 B, Appendix
				  D, Figure 2).
7. Edge Matching.
				  Edge matching is the matching of lines and areas between map sheets. With
				  digital data the match implies that each line ends with a node which is either
				  the same node or has the same coordinates of the node of the line that
				  continues onto the adjoining map sheet (see §1315 C, Appendix D, Figure
				  3).
8. Digital Mapping Product. The
				  product of digital mapping will be topologically structured digital data sets
				  that store map objects using Louisiana State Plane Coordinates and associated
				  attribute information with each object. The digital mapping product that a
				  parish or other user produces or receives may include a number of individual
				  data sets, or all data may be integrated in a single database. Attribute data
				  may be stored as part of the geographic data set or in an associated database.
				  Each graphic object will be attributed according to a specified labeling
				  scheme. Thus, a road could have only the road name stored as an attribute of a
				  road line (e.g., Louisiana Highway No. 30), or it could have road name, type of
				  road, road owner, right-of-way width, and other related information for each
				  line that represents the road. Similarly, an area representing a parcel might
				  only have the parcel identification number associated with it or it might have
				  all information that the parish or other users maintain on that property.
				  Associated information may be keyed in or merged into a data set from
				  information that has already been stored in a computer readable
				  format.
9. Coincident Features.
				  Coincident features are those which are in common between two or more data
				  layers. For example, if a political boundary is formed by a river bank, the
				  river bank and political boundary are coincident features. Coincident features
				  must be digitized only once. Regardless of the care taken in digitizing, slight
				  differences are inevitable if a feature is digitized more than once. These
				  differences lead to problems resulting in small "slivers" if the layers are
				  topologically joined. Coincident features, digitized once, can be placed into
				  master template coverages from which they can be retrieved when needed for
				  incorporation into another layer, or they can be taken directly from the
				  original coverage. In the above example, if the river was digitized first, the
				  arcs necessary for the political boundary can be selected and placed in the new
				  coverage.
10. Topological Editing.
				  Topological editing builds polygon and arc node topology by identifying areas
				  enclosed by arcs and creates a list of arcs which define each polygon boundary.
				  During editing, two or more coordinates within a specified tolerance of each
				  other (i.e., fuzzy tolerance) are snapped together and become the same
				  coordinate point. No distinction is made between interior arc coordinates and
				  nodes or between arcs. Because the fuzzy tolerance actually moves arc vertices,
				  understanding its relationship to coverage resolution is important. A dangling
				  node refers to the unconnected node of a dangling arc. Every arc begins and
				  ends at a node point. So if an arc does not close properly, or was digitized
				  past an intersection, it will register as a dangling node. During editing, all
				  unacceptable dangling nodes within a specified tolerance must be removed. In
				  some cases, a dangling node may be acceptable. For example, in a street
				  centerline map, cul-de-sacs are often represented by dangling nodes.