GEOG 480
Exploring Imagery and Elevation Data in GIS Applications

Lesson 6 Introduction


Lesson 6 provides an overview of accuracy assessment procedures and standards applied to remotely sensed mapping datasets intended for public use in the United States. In the context of this lesson, accuracy assessment refers primarily to geometric fidelity of the dataset, the degree to which the spatial coordinates of a data element agree with their “true” coordinates on the earth’s surface. However, in reference to image analysis, accuracy assessment also refers to the correctness of the thematic maps produced by land cover classification or change detection. Geometric accuracy is the focus of this lesson; classification accuracy is discussed in depth in Geography 883.

Accuracy assessment is a quantitative analysis of the spatial correctness of the dataset compared to the surface it represents. For most mapping products, there are also aesthetic standards for elements of quality which may not affect spatial accuracy, but can either enhance or detract from the experience of viewing the data or using it as a backdrop in GIS. The lesson material will focus on quantitative methods of accuracy assessment, but, for completeness, will also touch upon the qualitative. Together, the quantitative and qualitative evaluations are referred to by the broader terms, quality assurance and quality control (QA/QC).

A number of accuracy standards, used by public agencies and many private entities throughout the United States, will be presented in the textbook readings and summarized in the online course material. The study of standards and data specifications demands concern for minute details and precise use of terms and definitions. In this course, we have not been able to study all of the detailed elements of remote sensing technology and datasets addressed by most mapping standards; therefore, it’s important to try to get an overall sense of the major categories of issues being addressed. By the end of this lesson, the student should have an appreciation for the way remote sensing datasets are evaluated for geometric accuracy, and the way the results of those evaluations are (or at least, should be) reported to end users.

Lesson Objectives

At the end of this lesson, you will be able to:

  • describe and compare various federal and state standards for imagery and elevation data;
  • compute a quantitative accuracy assessment in accordance with FGDC standards;
  • perform visual quality assessment for both imagery and elevation data.


If you have any questions now or at any point during this week, please feel free to post them to the Lesson 6 Questions and Comments Discussion Forum in Canvas.