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Lecture 3
GIS Data Models, Data Formats, ArcCatalog and Data Management
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Outline
►GIS Data ModelsVectorRaster
►GIS Data Formats►Data Structure►The Geodatabase►ArcCatalog►Data Management
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Representing Physical Entities
► In a GIS, physical entities such as lakes, roads or vegetation type are represented in a simplified fashion by spatial features (i.e. polygons or lines).
► The spatial objects that represent an entity are determined by the person or organization creating the data based on:
1. The intended use of the data
2. The desired level of detail and accuracy.
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So what are Data Models?► The objects in a spatial database plus the relationships
among them.
► Provides a formal means of representing and manipulating spatial information.
► Two types of data are used to represent entities:1. Coordinate or geometric
data2. Attribute data
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Coordinate or Geometric Data►Used to define the spatial location and extent.► Frequently consists of a pair of numbers.► 1 or many pairs of coordinates represent the
shapes and boundaries that define objects.
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Attribute Data
► Use to capture non-spatial aspects of an entity.► Most often contained in a table► Attributes can be categorized as:
Nominal: Provide descriptive info. Ex. Color, names, types of soil. No implied order, size of quantity.
Ordinal: Imply rank order or scale. Does not represent differences in scale. Ex. Descriptive (short, medium, long) or numeric (1-100).
Interval/Ratio: Where both order and absolute differences in magnitude are represented. Ex. Length, weight, height or depth.
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GIS Data Models
►Common Spatial Data ModelsVectorRaster
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Vector Spatial Data Models► Points – A coordinate pair► Lines (arcs) – Ordered set of coordinate pairs that begin and
end with a node.► Polygons (feature with area) – Ordered set of connected
lines.
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Spaghetti Vector Data Models
► Early vector model►Unstructured – Does not
record or enforce connections between line segments or shared polygon boundaries.
►Results in inefficient and inaccurate analysis.
►Usually upgraded to a topological data model
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Topological Vector Data Models► Topology:
The study of geometric properties that do not change when the forms are bent, stretched or undergo similar transformations.Captures the relationship between features.
► 3 Types of Relationships:AdjacencyConnectivityContainment
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Advantages and Disadvantages ofTopological Vector Data Models
Advantages:► Familiar and intuitive representation for many kinds of data► Efficient (in terms of memory and computing)
representation for relatively sparse data► Offers very good resolution of linear and point features► Facilitates TOPOLOGICAL ANALYSIS
Disadvantages of Vector Data Model:► Compute-intensive when working with multiple overlays► Not good at representing continuous surface
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Raster Spatial Data Models
Defines the world as a set of cells in a grid pattern.
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Raster Cells
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Raster Compression
► With raster data, we must deal with storing data differently than vector to reduce volume.
► The dominant data compression techniques are:
run length coding quad tree compression
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Advantages and Disadvantages of the Raster Data Model
Advantages of a raster data model:• Very efficient for processing and analyzing multiple overlays (different
thematic layers)• More accurate and natural representation for continuous, smoothly-varying
information (such as topography)• Constant cell size and regular geometry facilitate some analysis and
modeling tasks--computing areas, for example, is just counting cells.• Best for use with probabilistic modeling
Disadvantages of raster data model:
• Data volume and redundancy -- dense grid of data involves large memory requirements and computer power.
• Difficult to resolve fine details (little to no variation of values of large area) better captured by vector data.
= OR
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Vector vs. Raster Data Models►Choice
depends on conditions and type of data you are trying to model.
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Triangulated Irregular Networks(TIN’s)
► Used to display and analyze surfaces. ► Contain irregularly spaced points that have x,y coordinates describing
their location and a z-value that describes the surface at that point. ► Can be created from several types of data including rasters, and point,
line, and polygon feature classes that have z-coordinate values.
Elevation Based TIN
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Vector vs. Raster vs. TIN’sDigital Elevation Example
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GIS Data Formats
►Types of files used to store and transfer spatial data.
►Most common file formatsShapefiles – Vector Coverages - Vector
Geodatabases - Vector and RasterGrids – RasterImages (Ex. Tiff’s, Jpeg’s, etc) – Raster
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Common File Formats
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Shapefiles► A shapefile is a feature class—it stores a collection of
features that have the same geometry type (point, line, or polygon), the same attributes, and a common spatial extent
► File-based data format native to ArcView® 3.x software
Viewed using a File Explorer
Viewed in ArcCatalog
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Coverages
► Coverages have a geometry type of point, line, OR polygon and represent a single thematic layer.
► A file-based data format native to ESRI's ArcInfo® Workstation software.
► The attributes and spatial relationships associated with a coverage feature class are stored in INFO-format tables.
► ALWAYS use ArcCatalog to move, edit or delete coverages.
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Geodatabases► The geodatabase is a container for storing spatial and
attribute data and the relationships that exist among them
► Format introduced by ESRI with ArcGIS® software ► Primary format we will be working with in this class.
Icons identify feature types
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Geodatabases and Data Organization
►Geodatabases can consist of:Feature DatasetsFeature ClassesAnnotation Feature ClassesRaster DatasetsNonspatial Tables
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Types of Geodatabases
► Scalable Functionality► 3 Types:
File Geodatabases: Stored as folders in a file system. Each dataset holds up to 1 TB of data. Fast performance, less restrictive editing locks and supported by many platforms.
Personal Geodatabases: Stored within Microsoft Access. Holds up to 2 GB of data.
ArcSDE Geodatabases: Stored in a relational database using Oracle, Microsoft SQL Server, IBM DB2, or IBM Informix. Requires the use of ArcSDE software. Unlimited in size and numbers of users.
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ArcCatalog► The application for browsing, managing and documenting geographic
data.► Create connections to drives that store data and maps.► Utilize drag and drop functionality to interface with ArcMap.
Catalog Tree Preview Pane
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ArcCatalog: Data Connections
Direct Connect
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ArcCatalog: Metadata
►Data about data► Provides
information about a dataset
►Certain properties generated automatically
►Other properties require manual entry
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Data Management
►Know where your data is! ►Best location is on the root of the C or D
drive. ►Stay away from spaces in folder or file
names. Use “_” instead.►Limit characters►Create folders as needed to keep data
organized!
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Data Management (Cont.)
► If you move the ArcMap document, the data does NOT go with it.
► If you move or rename the data layers OR the folders they are stored in, the ArcMap document will NOT know where to find them.
► Use
Data is stored separately from the ArcMap document (.mxd file).
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Updating the Data Source► When layer is grayed out, click on “Layer Properties”.► Click “Set Data Source…”► Navigate to current location of data.