Geoscience Reference
In-Depth Information
imperviousness information maps, contours, 2D and 3D elevation maps, digital
orthographic aerial photos, and piping network maps of the drainage area can be
used to generate input parameters for an urban storm-water model (Seth et al.
2006
). According to Van Der Laan (
1992
), a raster-based GIS has advantages
over a vector-based GIS because virtually all types of data (attribute data, spatial
data, scanned data, and DEMs) can be represented in raster format. Along with
spatial data GIS also includes databases. These databases are comprised of
different parametric data (e.g. soil permeability, precipitation etc.) which can
be linked to the corresponding spatial data. Metadata is an important aspect of GIS.
Metadata can be regarded as valuable information regarding the actual data.
Data acquisition is the cornerstone of any water resources GIS project
(Tsihrintzis et al.
1996
). GIS data is available from numerous sources. They may
be governmental, private, academic etc. There are numerous GIS data clearinghouses
(e.g. GIS Data Depot, Geospatial One Stop etc.) on the internet that can provide GIS
data (Seth et al.
2006
). Watershed resource inventories can provide GIS data on
soils, land cover, land use, topography, geology, climate, demographics, socio-
economics, water resources and water quality (Grunwald
2007
). Aerial photographs
are a type of data which show a bird's eye view of the study area. The National
Aerial Photography Program (NAPP) and the National Agricultural Imagery Pro-
gram (NAIP) are good sources for aerial photographs (Seth et al.
2006
). Knowledge
about GIS data is very important when one goes shopping for data. Though there
is a lot of data out there one needs to be very careful in choosing the right type
and amount of data for GIS operations. One of the major hurdles for the full
realization of the potential of GIS is having standardized and more accessible
databases (Seth et al.
2006
).
If the data is not readily available then it can be created. In other words if the
existing data does not meet the requirements for GIS analysis or GIS based
modeling then the required data can be created. For example piping network data
can be derived from hardcopy maps (Seth et al.
2006
). These hardcopy maps can be
scanned and digitized. The Computer Aided Drafting (CAD) drawings which are
created using the above mentioned processes can then be georectified and overlaid
on drainage area maps. CAD software like AutoCAD and Microstation are very
useful in creating and updating these CAD files. Data can also be created using a
Global Positioning System (GPS). Contour maps can be generated from DEMs
(Seth et al.
2006
). Soil imperviousness can be generated from IKONOS satellite
images using various statistical techniques such as Fisher Discriminant Analysis
(Herold et al.
2003
). Also, land use GIS maps can be generated using data from
regional and local agencies (Seth et al.
2006
).
1.2.2 GIS Operations
A detailed discussion of the GIS operations is beyond the scope of this chapter
therefore a very brief insight for the reader follows. GIS operations include data
