NRSC 2230 / GEOG 2750

GIS Data Structures / Vector Formats

Overview

One sense of the term data structure is used to describe the manner of storage and retrieval of spatial data.  The two commonly used structures are the Raster and the Vector structures.  Each of these has its advantages and disadvantages. We will also look at the more commonly used vector formats in ArcGIS, the shapefile and the coverage.

Learning Outcomes

Upon successful completion of this topic, you will be able to:

  • Explain the characteristics of the raster data structure
  • Explain the characteristics of the vector data structure
  • Explain the main characteristics of the ArcGIS shapefile data format
  • Explain the main characteristics of the ArcGIS geodatabases
  • Explain the main characteristics of the ESRI coverage data format

Raster and Vector

Activity 1 – Raster vs Vector search

Please use your favourite search engine (e.g. google etc.) to find information regarding the differences, advantages of each structure in GIS applications. How are the data stored and presented? What kinds of applications are suited to one vs the other? The following site is a good starting point.

Wikipedia

Activity 2 – Research Findings / Comment

Write two short paragraphs in a blog entry describing your findings regarding the use and suitability of raster data and vector data in GIS applications.  Indicate how your findings can be applied in your area of study.  Please provide links to the sites you found most useful.  Please title this blog entry “Raster and Vector Data”.

Shapefile

A shapefile stores nontopological geometry and attribute information for the spatial features in a data set. The shapefile consists of a minimum of three files, namely:

  • A main file with a .shp extension. The contents of this file describe each feature with a list of its vertices.
  • An index file with a .shx extension.  This file is used to facilitate quick searches through the main file.
  • A dBASE table with a .dbf extension. This table contains feature attributes with one record per feature.

Geodatabase

An ArcGIS geodatabase is a collection of geographic datasets of various types held in a common file system folder, a Microsoft Access database, or a multiuser relational DBMS.  The fundamental contents for every geodatabase are tables, features, and rasters.

Coverage

A coverage is a combination of system directories and associated sub-files.  A coverage exists in a folder that contains a sub-directory named info and a system directory that is also the coverage name.  Inside the coverage directory must contain at least two files namely:

  • A boundary file with the extension .bnd.  This file stores the geographic extents of the data
  • A control point file with extension .tic.  This file stores the location of the geographic reference (TIC) points of the data.

The coverage differs from the shapefile in two important ways, namely:

  • It implicitly stores topological relationships between features
  • It does not allow overlaps or duplicates

Activity 3 – Geodatabase research

Search the ArcGIS Resource Center Desktop 10 Help for information on ‘Table Basics”.  Use a post in your blog to explain the role relationships play in ArcGIS geodatabases.

Activity 4 – Comments on Geodatabase post

Review at least one of your colleague’s post on Table relationships and leave a comment