Digital Spatial Data

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Digital Spatial Data

• Engineering Applications of GIS
• Civil and Environmental Engineering
• CEEn 514

Francisco Olivera PhD, PE Department of Civil and
Environmental Engineering Texas AM University
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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.

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Data Types

• Features
• Point datasets
• Line datasets
• Polygon datasets
• Surfaces
• Grid datasets
• TIN datasets
• Images datasets
• Networks
• Simple dentritic networks
• Simple loop networks
• Geodatabase
• A collection of feature, surface, and network
  datasets with defined relationships between
  features of different datasets object oriented

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Features

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

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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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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.
• Shared polygon boundaries are stored only once.
• Coverages have topologic data structures.
• Cartographic data structures
• Stores the geometry of the features.
• Points can coincide.
• 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
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 Geodatabases

• A geodatabase is a relational database that
  connects several feature datasets with
  accompanying relationships

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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.
• Geodatabases
• A collection of datasets is stored in a database
  file. Typically on a PC platform this will be an
  Access database file with a .mdb extension.

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Storing Datasets

• As GIS has evolved over the years there have been
  many different ways to store datasets. The
  following are the most commonly supported by
  ArcGIS

point
Shapefile.shp Shapefile.shx Shapefile.dbf
line
polygon
Shapefile.lyr (references data with accompanying
symbology)
point
line
Image.tif
polygon
Table file(.txt, .dbf, others)
Geodatabase.mdb
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Managing Datasets

• ArcCatalog
• In version 9.x of ArcView one of the primary
  applications is ArcCatalog. This is like a
  Windows Explorer utility that lets you display,
  and view all types of geographic data. Each
  dataset type is associated with an icon and
  hopefully you will soon be able to recognize the
  difference.
• Renaming, Copying and Moving
• Be careful about renaming and always use ArcGIS
  to do it because some information can be lost
  from folders you may not know to be related.

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ArcCatalog

• Connections
• Icons
• Contents
• Preview
• Geography
• Table
• Metadata

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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.

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Symbology

• Symbology of features and rasters includes
• Colors
• Markers (icons)
• Sizes
• Widths
• Angles
• Patterns
• Transparency
• Others
• This is how we make features look like what
  they represent on a map

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Scale and Symbology

• Scale effects the way features are displayed on a
  map
• Cities
• Small scale a point
• Large scale a polygon

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Attributes and Symbology

• Often you will control the way features look
  based on some attribute in the table

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Layer Properties