Digital Spatial Data

1
Digital Spatial Data

• Francisco Olivera, Ph.D., P.E.
• Department of Civil Engineering
• Texas AM University

2
Definitions

• Digital Spatial Datasets Synthesis -- in
  electronic format -- of geographic (map) and
  tabular (table) information.
• Data structure method used to organize and store
  digital spatial datasets.

3
Data Types

• Features
• Point datasets
• Line datasets
• Polygon datasets
• Surfaces
• Grid datasets
• TIN datasets
• Images datasets
• Networks
• Simple dentritic networks
• Simple loop networks

4
Features

• All points required to define the feature
  geometry have to be stored as part of the feature
  definition.

5
Features

• Point datasets

One-to-one relation between features in the map
and records in the table.
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Features

• Line datasets

One-to-one relation between features in the map
and records in the table.
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Features

• Polygon datasets

One-to-one relation between features in the map
and records in the table.
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Surfaces

• Grid datasets

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Surfaces

• TIN datasets

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Surfaces

• Image datasets

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Networks

• Simple dentritic networks

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Networks

• Simple loop networks

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Data Structures of Features

• Topologic data structures
• Store (1) the geometry of the features, and (2)
  the spatial relationship between connecting or
  adjacent features (i.e., topology) in tabular
  format.
• Points do not coincide.
• Lines are simple.
• Polygons are simple and space-filling (i.e., no
  overlaps or empty spaces).
• Shared polygon boundaries are stored only once.
• Coverages have topologic data structures.
• Cartographic data structures
• Stores the geometry of the features.
• Points can coincide.
• Lines can be complex.
• Polygons can be complex, and not necessarily
  space-filling.
• Shared polygon boundaries are stored as part of
  the definition of each of the adjacent polygons.
• Shapefiles have cartographic data structures.

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Data Structure of Features

• A line is an open sequence of points in which the
  first and last points are called nodes, and the
  remaining intermediate points are called vertices.

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Data Structure of Features

• Simple lines

• Complex lines

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Data Structure of Features

• Simple polygons

• Complex polygons

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Data Structure of Features

• Not space-filling polygons

• Space-filling polygons

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Data Structure of Features

• Line and polygon topology

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Data Structure of Surfaces

• Grid datasets
• Cellular-based data structure composed of square
  cells of equal size arranged in rows and columns.
• Grid definition requires (1) the coordinates of
  the upper-left corner, (2) the cell size, (3) the
  number of rows, (4) the number of columns, and
  (5) the value at each cell.
• Cells that do not store any value are called
  NODATA cells.

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Data Structure of Surfaces

• Triangular Irregular Network (TIN) Datasets
• Dataset constructed by connecting points -- for
  which the TIN parameter is known forming
  triangles.
• Triangle sides are constructed by connecting
  adjacent points so that the minimum angle of each
  triangle is maximized.
• Triangle sides cannot cross breaklines.
• The TIN format is efficient to store data because
  the resolution adjusts to the parameter spatial
  variability.

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Data Structure of Surfaces

• Triangular Irregular Network (TIN) Datasets

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Data Structure of Surfaces

• Image datasets
• ARC Digitized Raster Graphics (ADRG)
• Windows bitmap images (BMP) .bmp
• Multiband (BSQ, BIL and BIP) and single band
  images .bsq, .bil and bip
• ERDAS .lan and .gis
• ESRI Grid datasets
• IMAGINE .img
• IMPELL Bitmaps .rlc
• Image catalogs
• JPEG .jpg
• MrSID .sid
• National Image Transfer Format (NITF)
• Sun rasterfiles .rs, .ras and .sun
• Tag Image File Format (TIFF) .tiff, .tif and
  .tff
• TIFF/LZW

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Data Structure of Networks

• Simple dentritic networks
• System of simple lines -- called links --
  connected at their nodes.
• All links point towards (or away-from) a given
  node called sink.
• One-to-one relation between From-Node (or
  To-Node) and link.

A
C
B
1
2
D
3
4
E
5
F
F is the network sink.
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Data Structure of Networks

• Simple loop networks
• System of simple lines -- called links --
  connected at their nodes.
• Links can point in either direction or in both
  directions.

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Storing Datasets

• Features
• Coverages are stored partially in their own
  folder and partially in the common INFO folder.
• Shapefiles are stored in at least three files
  (with extensions .shp, .shx, .dbf) and up to
  seven files (with extensions .sbx, .sbn, .ain and
  .aih).
• Surfaces
• Grid and TIN datasets are stored partially in
  their own folder and partially in the common INFO
  folder.
• Image datasets are stored in different ways
  depending on the image format.
• Networks
• Simple dentritic and loop networks are stores as
  a line dataset of links, a point dataset of
  nodes, and a topology file.

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Storing Datasets

• Structure of a folder containing different types
  digital spatial data.

Image.tif Shapefile.shp Shapefile.shx Shapefile.d
bf
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Managing Datasets

• Renaming
• Always use ArcInfo or ArcView utilities to rename
  coverages, shapefiles, grids and TINs because
  some information is internally stored with the
  dataset name.
• Images can be renamed using the operating system
  utilities.
• Copying and Moving
• Always use ArcInfo or ArcView utilities to copy
  and move coverages, grids and TINs to make sure
  the information stored in the INFO folder is
  included.
• Shapefiles and images can be moved or copied
  using the operating system utilities, making sure
  all the files are included.

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Sharing Datasets

• Interchange files
• Coverages, grids and TINs are shared as
  interchange files.
• An interchange file is a single file -- with
  extension E00 -- that includes all information
  stored in the dataset folder and its share of
  information contained in the INFO folder.
• If a limit is set on the size of the interchange
  file, then several smaller files (i.e., E00, E01,
  E02, ) are generated rather than one single
  file. This option was common when storage media
  had limited capacity.
• An interchange file is obtained by exporting a
  coverage, grid or TIN. In turn, a coverage, grid
  or TIN is obtained by importing an interchange
  file.
• Compressed (zipped) files
• To make sure that all files are included,
  shapefiles and images can be shared as compressed
  files.