Lecture 3

GIS Data Models, Data Formats, ArcCatalog and Data Management

Outline

►GIS Data ModelsVectorRaster

►GIS Data Formats►Data Structure►The Geodatabase►ArcCatalog►Data Management

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.

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

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.

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.

GIS Data Models

►Common Spatial Data ModelsVectorRaster

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.

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

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

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

Raster Spatial Data Models

Defines the world as a set of cells in a grid pattern.

Raster Cells

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

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

Vector vs. Raster Data Models►Choice

depends on conditions and type of data you are trying to model.

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

Vector vs. Raster vs. TIN’sDigital Elevation Example

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

Common File Formats

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

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.

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

Geodatabases and Data Organization

►Geodatabases can consist of:Feature DatasetsFeature ClassesAnnotation Feature ClassesRaster DatasetsNonspatial Tables

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.

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

ArcCatalog: Data Connections

Direct Connect

ArcCatalog: Metadata

►Data about data► Provides

information about a dataset

►Certain properties generated automatically

►Other properties require manual entry

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!

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).

Updating the Data Source► When layer is grayed out, click on “Layer Properties”.► Click “Set Data Source…”► Navigate to current location of data.