Introduction to Geographic Information Systems (GIS)

Organization of presentation Basics of GIS GIS data at the New Jersey Department of Environmental Protection

Basics of GIS

Geographic Information Systems (GIS) GIS facilitates visualization and analysis of spatial data Spatial data are stored in map layers GIS facilitates the visualization and analysis of spatial data.  In 1998, Burrough defined GIS as a "set of tools that collect, store, retrieve, transform, and display spatial data from the real world for a particular set of purposes". In a GIS, spatial data are stored in a map layer.  Conceptually, a map layer is a file containing all the information regarding one aspect of a data set, such as a street network.  For instance, let’s take a community in North Carolina, call it reality, and break it down into map layers that would be useful in a GIS.  One map layer would contain the street network.   A second map layer would show the location of buildings, perhaps doctors offices.  A third map layer would display all the customers in the community -- you may want to think of them as patients.  Other map layers could include a land cover layer delineating environments ideal for vector breeding, or …

Coordinate Systems Spatial data are referenced to locations on the earth’s surface using coordinate systems Ensure all map layers share a common coordinate system Recognized global coordinate systems consist of: A Spheriod: a mathematical description of the earth’s shape A Map Projection: a mathematical conversion from spherical to planar coordinates In a GIS, spatial data need to be referenced to locations on the earth’s surface. Usually this is done using a coordinate system such as a longitude-latitude.  However, alternative coordinate systems can be used as well. For instance, some population level health data, such as birth rates, are referenced using zip codes or county numbers, while some individual level data are referenced using an x,y coordinate system the way magnetic resonance imaging maps the brain. It is imperative to ensure all your map layers share a common coordinate system. If they do not, you will not be able to overlay your map layers and conduct an analysis. If your map layers use different coordinate systems, usually they can be converted to one in common.

Map Projection

Map Projection

Scale Tells how map distance relates to real world distance Map Scale: ratio of map distance to actual ground distance 1:10,000 (1 map cm = 10,000 real cm) Small scale (1:100) vs. large scale (1:10) Scale Bar: graphic display of map scale

Resolution The accuracy with which a given map scale can depict the location and shape of map features Larger the map scale, the higher the resolution As map scale decreases, resolution diminishes and feature boundaries are smoothed, simplified, or not shown at all. Rule of thumb: error = 2% of map scale Resolution plays a large role in GIS, especially in raster-based modeling

Raster-based GIS Data stored in a ‘regularized grid of cells covering an area’ Grid cells called picture elements or ‘pixels’ Nodes, Arcs, Areas Raster-based GISs use a 'regularized grid of cells covering an area' to store and display an image and its associated attributes.  Each cell in the grid is a picture element called a pixel. This is similar to the pixels comprising your television or computer screen.  Each pixel holds all the information for that location in the image. 

Vector-based GIS Image and data stored separately Data: attribute table Image: points, lines, polygons Vector-based GISs store spatial images and the associated spatial data separately. In a vector-based GIS, spatial data, such as county birth rates, are stored in an attribute table, while the spatial image is displayed in a separate window. Vector-based images are constructed using points, lines and polygons.

Summary GIS facilitates visualization and analysis of spatial data Spatial data are stored in map layers Most GIS programs are raster- or vector- based Raster - data and image stored together in regularized grid made of pixels Vector - data and image stored separately; points, lines and polygons

GIS and Water Quality data at the New Jersey Department of Environmental Protection http://www.nj.gov/dep/

NJDEP - GIS The NJDEP – GIS Department (http://www.nj.gov/dep/gis/) provides GIS files for state administrative areas, hydrology, geology, land use, etc., such as: Counties Digital Elevation Grid Hydrography Watersheds Water Quality Monitoring Stations

NJDEP - Water Monitoring & Standards The NJDEP Office of Water Monitoring & Standards (http://www.state.nj.us/dep/wmm/) oversees the Bureau of Fresh Water and Biological Monitoring . This bureau is in charge of monitoring the ambient conditions of the state's fresh and ground water resources. This monitoring includes : regular sampling through a statewide network consisting of 115 surface water monitoring stations, 820 benthic macroinvertebrate biological stream monitoring stations, 100 fish assemblage biological stream monitoring stations, and 150 ground water stations.

ESRI arcGIS at UNC UNC GIS software includes ESRI arcGIS version 9.0, 9.1 , 9.2 , 9.3 Getting Started: http://www.lib.unc.edu/reference/gis/getting_started.html Technical support research@unc.edu (919) 962-HELP Data Sources: http://www.lib.unc.edu/reference/gis/ Amanda C. Henley, GIS Librarian amanda.henley@unc.edu (919) 962-1151