format, and resolution size of pixels are examples of possible areas for format error.
Expediency and cost often require data reformation to the "lowest common denominator" for
transmission and use by multiple GIS. Multiple conversions from one format to another may
create a ratchet effect similar to making copies of copies on a photo copy machine.
Additionally, international standards for cartographic data transmission, storage and retrieval
are not fully implemented.

g. Accessibility

Accessibility to data is not equal. What is open and readily available in one country may be
restricted, classified, or unobtainable in another. Prior to the break-up of the former Soviet
Union, a common highway map that is taken for granted in this country was considered
classified information and unobtainable to most people. Military restrictions, inter-agency
rivalry, privacy laws, and economic factors may restrict data availability or the level of
accuracy in the data.

h. Cost

Extensive and reliable data is often quite expensive to obtain or convert. Initiating new
collection of data may be too expensive for the benefits gained in a particular GIS project and
project managers must balance their desire for accuracy the cost of the information. True
accuracy is expensive and may be unaffordable.

42. Errors Resulting from Natural Variation or from Original Measurements

Although these error sources may not be as obvious, careful checking will reveal their
influence on the project data.

a. Positional accuracy

Positional accuracy is a measurement of the variance of map features and the true position of
the attribute (Antenucci and others 1991, p. 102). It is dependent on the type of data being
used or observed.. Map makers can accurately place well-defined objects and features such as
roads, buildings, boundary lines, and discrete topographical units on maps and in digital
systems, whereas less discrete boundaries such as vegetation or soil typemay reflect the
estimates of the cartographer. Climate, biomes, relief, soil type, drainage, and other features
lack sharp boundaries in nature and are subject to interpretation. Faulty or biased field work,
map digitizing errors and conversion, and scanning errors can all result in inaccurate maps for
GIS projects.

b. Accuracy of content
Maps must be correct and free from bias. Qualitative accuracy refers to the correct labeling

and presence of specific features. For example, a pine forest may be incorrectly labeled as a
spruce forest, thereby introducing error that may not be known or noticeable to the map or