Introduction to

GPS & GIS

Jason Biagio

GIS Manager/Administrative Analyst

City of Porterville

GPS

Global Positioning System is a 24-satellite navigation system placed in orbits at about 3.75 times the radius of the Earth, which provides location and time information in all weather conditions, anywhere on or near the earth where there is an unobstructed line of sight to four or more GPS satellites. The satellites are arranged in six orbital planes with four satellites in each plane.

GPS - cont.

The basis of GPS is "triangulation" from satellites. We're using the word "triangulation" very loosely here because it's a word most people can understand, but purists would not call what GPS does "triangulation" because no angles are involved. It's really "trilateration." Trilateration is a method of determining the relative positions of objects using the geometry of circles, spheres, or triangles. Three satellites and their respective “spherical intersections” determine two possible locations of an object on the earth’s surface. A fourth satellite is used to determine which of the two is the actual point and for time tracking.

To "triangulate," a GPS receiver measures distance using the travel time of radio signals (which travel at the speed of light minus atmospheric interference)

GIS

A geographic information system (GIS) lets us visualize, question, analyze, and interpret data to understand relationships, patterns, and trends.

GIS benefits organizations of all sizes and in almost every industry. There is a growing interest in and awareness of the economic and strategic value of GIS.

Cost Savings from Greater Efficiency
Better Decision Making
Improved Communication

Practical Application

Outline Problem: (Water Shortage @ East Porterville)

As many of you know, California has suffered greatly in recent years with lack of rain and snow which has led to shortages all over the state. One of the most impacted area is our backyard, East Porterville. When you combine descending aquifers (lowering of the water table) and shallow domestic wells, many residences simply ran out of water.

Next steps; how to track and plan for resolution?

Traditional Approach

Traditional Approach and shortcomings:

The traditional approach would most likely include the development of a spreadsheet or database to track residences that are without water, something like so:

This is great but does not give us a “picture” of the larger problem or enable us to see trends. For instance, if you were a resident in East Porterville and your neighbor’s well ran dry, chances are that your well will run dry soon as it draws from the same water source. With tabular data it is very difficult to see this in action. Let’s see if GIS can help us out.

GIS Approach

Problem Solving with GIS and advantages (visualizing greatest need, trends, forecasting, efficient response…etc.)

Seen below is a map of Porterville in all its glory…
The bold white line demarks the City Limit Line.

GIS Approach - cont.

Navigate to the icon that looks like layers in the upper left corner of the map. The Layers will expand and you will need to navigate to Water Related --> "Water Shortage per Water Dept" and "Requests for Assistance". Turn both layers on. The red dots represent properties whose wells have failed. The yellow dots represent properties whose wells are failing. The yellow dots are “geocoded” from the addresses in the list. Geocoding a way of interpolating geographic location based on address to yield a lat/lon point, the same lat/lon used in the GPS system. You can see much more clearly that East Porterville is in need of help. Do you notice any other trends?

GIS Approach - cont.

Next we will add all the water utility accounts. You can see that there are some properties served by the City outside the City Limits. There are a few explanations for this, but to simplify the discussion, the City serves schools with water for Fire Prevention. On occasion, residences adjacent to schools also connect to water, even though they are outside the City Limits.

GIS Approach - cont.

Now let’s zoom in a bit. The red dots indicate properties that are confirmed to be without water. The yellow dots indicate properties with failing wells. See a trend? The blue lines indicate existing water mains (infrastructure).

Based upon this information, how many properties could we connect in short order as an emergency fix?

Closing

We briefly covered GPS & GIS in broad strokes to introduce you to the technologies that will continue to help serve Environmental Sciences (and just about any other discipline) moving forward into the future.

We have only scratched the surface as to what GIS can do and its usefulness with visualizing a problem.

It is my hope that this knowledge may inspire you to purse more understanding of GIS and leverage its capabilities in your various pursuits.

Thank you for your attention and thoughtful comments.

If you would like more information, kindly email me at jbiagio@ci.porterville.ca.us and I will answer your questions as thoughtfully and thoroughly as possible.