What is a geographic information system?

More commonly known by its acronym, GIS is a tool used to relate spatial, temporal and tabular data,such as rainfall totals, population statistics or land use, for a common geographic study area.

“GIS is a collection of different types of data that, when georeferenced, provide insight about various phenomena in the area of interest,” says Tim Minor, a geospatial scientist in the Division of Earth and Ecosystem Sciences at the Desert Research Institute.

The Walker Basin Project, for example, involved the integration of many spatial and tabular data sets related to irrigation delivery systems, the associated streams and rivers, and how topography, geology and vegetation affected water flow. “These are the types of data we integrate to help the surface and groundwater modelers conduct their analyses,” Minor says.

Topography

GIS researchers gathered a wide variety of existing spatial and tabular data sets from local, state and federal agencies, but also had to collect new data. One such data set was high-resolution Light Detection and Ranging (LiDAR) data, which uses an active laser system to measure distance returns from the ground surface back to the instrument onboard an airplane. LiDAR data were collected over the major sub-basins in the Walker River Basin, providing a very detailed description of the area’s topography. Combined with high-resolution aerial photography and satellite imagery, this information allowed the GIS group to create a detailed snapshot of the surface characteristics of the sub-basins, including Mason and Smith valleys.

Researchers constructed an extensive GIS database of the entire Walker Basin,
with data sets from federal, state and local agencies combined and integrated with derivative data sets. The result is a scalable, georeferenced collection of spatial data representing a wide variety of spatial and temporal features, as well as tabular information for the entire Walker Basin. The principal base layer for the development, processing and analysis was one-foot natural color aerial photography, complemented by six-inch resolution imagery of the Yerington area.

Water Supply

GIS provides an effective tool for integrating data related to irrigation delivery systems, serviced agricultural fields, and the water rights that control the distribution of water. Surface and groundwater parameters are combined to provide a better understanding of the various sources of irrigation water and the subsequent distribution of these waters for agricultural use. Agricultural fields serviced by a common delivery mechanism (irrigation ditch or wells) can be aggregated into hydrologic response units (HRUs) to assist modelers in the characterization of the delivery system and the water balance.

Infrastructure

To help create a complete picture of the various spatial and tabular data that characterize the study area, infrastructure data such as parcels, the Public Land Survey System (PLSS), landownership, roads and administrative boundaries are also integrated into the GIS database. This type of data allows the researchers to relate topographic, hydrologic, and vegetation phenomena to specific map units and properties in the study area.

These three data sets, when combined, produce a composite image as displayed below.