Quality is a concept often discussed and frequently misinterpreted. In the environmental consulting industry, quality is an aspect of the job which is extremely important for many reasons. This month's column presents some ideas on designing a quality control system for products generated using a GIS for environmental programs.
      During an environmental investigation, cleanup criteria are determined from the knowledge gained through site investigations. A typical site investigation includes statistical and other types of analyses of samples collected in the field to define the nature and extent of contamination. If the sampling is not of sufficient quality to adequately define the problem, the cost of cleanup increases significantly. If the products generated to analyze the information required to make a decision are not of adequate quality - measured in terms of precision, accuracy, completeness, and comparability - the entire decision process is in question. In the environmental consulting business, quality control is (or at least, should be) a key component of the daily grind.
      One standard for defining the minimum requirements for a quality system for environmental programs is the ANSI/ASQC standard, Quality Systems Requirements for Environmental Programs. This standard includes several definitions and guidelines for quality assurance and quality control procedures specifically as they relate to environmental programs. This standard addresses, in part, the quality system elements needed to plan, implement, and assess environmental data operations, including the collection, handling, analysis, and evaluation of environmental-related data.

Definitions of Quality-related terms
Some definitions are provided in the appendix of the ANSI/ASQC standard document. Several of those terms relevant to the topic of this column are presented:
Quality = "the totality of features and characteristics of a product or service that bear on its ability to meet the stated or implied needs and expectations of the user (customer)."
Quality Assurance = "an integrated system of management activities involving planning, implementation, assessment, reporting, and quality improvement to ensure that a process, item, or service is of the type and quality needed and expected by the customer."
Quality Control = "the overall system of technical activities that measures the attributes and performance of a process, item, or service against defined standards to verify that they meet the stated requirements established by the customer."
      Recently, topics related to estimating data quality and methods for measuring quality in a GIS setting are garnering much attention. Most of the efforts to date, however, have focused on ways to measure and improve the quality of data stored in a GIS database. There is very little information available regarding the topic of quality assurance with respect to GIS output products.
      In the environmental consulting arena, GIS output products are frequently used to evalute and present the findings from a site investigation. For example, many maps are generated using the GIS to present results of sampling and to determine depth to bedrock, water table elevations, contaminant concentrations, and other features of concern. A well-defined quality assurance program is key and crucial to the effective use of GIS output products in support of an environmental investigation.

Establishing Quality Standards
In order to measure the quality of a GIS output product, it is first necessary to establish a measurement standard. It is not always obvious how this should be accomplished. Some criteria to be considered in a quality standard for a GIS-produced map, ranked in order of importance, include:
• data accuracy and completeness
• correctness of interpretation
• cartographic presentation
• visual appeal
      Data accuracy and completeness imply that the information presented on the map includes all required data points, properly loaded into the GIS database and reflecting the true nature of the phenomena being modelled. For example, a map of water levels for the month of July should include all the wells from which water levels were collected in July. The water levels for each well should be posted at the correct location indicating the July water level for that well. The quality of a GIS-produced map is seriously degraded if any required data points are not included or contain incorrect attribute values such as a transposed water level.
      Correctness of interpretation involves verifying that a product created from some analytical operation on the data was completed properly. Contours generated from spot elevations or from a modelled elevation surface should represent the actual topography to the level of precision allowed by the raw data points. If a series of operations were conducted, the end result should accurately reflect the real-world phenomena being modelled. For instance, if surface runoff is calculated from flowpath analysis on a modelled topographic surface, it is necessary to first determine that the surface is accurately modelled, and that subsequent GIS operations adequately portray the flow paths and flow directions that are likely to occur during a runoff event over that topographic surface.
      Aspects of a quality cartographic presentation include a proper title block, map legend, scale bar or representative scale, and north arrow, as well as the proper, standardized use of symbols, patterns, and colors.
      Visual appeal is also a measure of quality, although it is probably the most difficult component to measure due to its subjective nature. There are some general guidelines to follow and some excellent resources for providing advice on how to best present data graphically. Cartography textbooks, especially the more recent editions which include chapters on computer mapping, are a good source for this sort of information.

Maintaining Quality Control
Procedures for maintaining quality control are essential when using GIS technology to support environmental investigations. This is especially true as projects grow in size and complexity. Some of the procedures that have been developed for quality control in document production can be effectively applied to GIS map production.
      An example of a GIS quality control procedure includes the implementation of a formal review process. The review process starts with a submittal sheet with specifications for the map(s) to be produced. The submittal sheet should spell out specific requirements as completely as possible before any processing begins. Those requirements include items such as map sheet size, orientation, base data layers to include, a title, figure number, and date due to the customer. It might also include date due for draft version to review, number of final copies, ultimate purpose, and other comments or instructions that might guide the GIS production staff towards the goal of a high-quality output product. After the first draft of the map(s) is produced, a thorough technical review occurs. Again, a form should be used to guide the reviewer and document any errors or shortcomings. The review process should be stringently enforced and adequate time should be allowed to perform a comprehensive review.
      When GIS quality assurance procedures are implemented and are being followed as routine business practice, the quality of products generated using a GIS will improve considerably.

About the Author:
Damon Judd is manager of GIS and computer applications for RUST Environment and Infrastructure in Broomfield, Colo. He can be reached at 303-469-6660.

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