Sampling - Field Sampling: Principles and Practices in Environmental Analysis - page 116

of the Earth's surface. The resolution, which depends on the portion of the spectrum
needed, is typically between 30 and 60 meters. When ordering an image, both the
location of the area of interest and the portions of the spectrum to be recorded must be
specified [7-9].
5.5. GEOGRAPHICAL INFORMATION SYSTEMS
When developing a sampling plan and collecting historical data about a field a question
to ask is if there is a GIS for the field and the surrounding areas. A GIS may contain
important information about cadastral questions, such as easements and rights-of-way;
the natural environment, such as hydrology, topography, vegetation, watersheds, and
wetlands; and utilities, such as water lines. This information can be invaluable in
developing and carrying out a sampling plan. It can save time and money, especially if it
avoids breaking a power line or similar underground facility.
Any system that makes a map or representation of the Earth's surface can be a GIS.
Today, however, it is generally understood that GIS refers to maps and other data stored
digitally on media that can be read and analyzed by computer. Such systems allow the
addition of any digital information to the map. This additional information can then be
displayed in a variety of different ways to help researchers understand phenomena
occurring on or below the Earth's surface. Such maps are said to be thematic.
In making thematic maps GIS makes use of elements from other mapping tools. The
most important of these is CADD and AM/FM. CADD is computer-aided design and
drafting, the map-drawing capabilities of which are included in GIS, but it does not have
data correlation capabilities. For instance, when looking at a hazardous waste field, GIS
can be used to determine how much of it is in a flood-prone area, while CADD cannot.
AM/FM is automated mapping/facilities management, which is used extensively for
mapping networks and network element characteristics. Again, data analysis is better
carried out using GIS. Any information about a field that is in either of these two formats
can be easily imported into a GIS system.
The thematic maps produced using GIS work a little like having the base map and
making transparent overlays for it. Each overlay would contain data of interest. Although
the data could thus be visually observed they could not be analyzed in relation to the base
map or to other layers; the GIS system allows for this. In addition, GIS systems allow for
the addition and removal of one or more layers as needed.
For sampling, the most important feature of GIS is the ability to display sampling sites
and their characteristics on a map of the field being sampled. This allows the sampling
sites to be coordinated with other features of the environment, such as water flow. This is
important because water movement may indicate other areas that need to be sampled or
watched.
Information displayed on a map can be entered manually into a computer system, in
the form of tables, for example. Alternately, it can be obtained directly from any digital
source of information. For instance, data obtained by remote sensing from aircraft or
satellites. A familiar example of this use is the display of weather. The daily weather
report incorporates this type of technology. Population densities, lightning strikes, and