Step 1: What is a GIS?
Let’s begin by talking about what a Geographical Information System is. A really good way to understand that, is to look at what GIS was! Prior to GIS, it was common for people to create custom maps to help them solve geographical problems. GIS is still used to create custom maps – it just does that more efficiently and effectively than the old way.
I want to show you two mapping projects from the history books. The first is an Epidemiology project from the 1850s and the second is an Environmental Planning project from the 1960s. As I go through the studies I’ll point out some important parallels with present-day GIS. The techniques used in these projects are both simple and logical. I hope you take the time to understand them. Even though they’re paper based, these two studies can form a fantastic foundation for understanding some of the things you can do with GIS, and also, importantly, some of the issues you’ll be faced with when you do your own GIS project …
Dr John Snow’s 1854 Cholera study included a mapping exercise is important to the study of GIS. During the outbreak over five hundred people in the Soho district of London died in just ten days. Simplistically, with the aid of a map, John Snow was able to convince local officials that a waterwell was the source of the infection. They removed the pump handle from the well and the outbreak ended.It’s not quite that simple though. A purely GIS-style technology solution would not have yielded a result that would have convinced Town Officials to remove the pump handle. Look out for four parallels with modern-day GIS…
- Parallel 1: He mapped where people were when they became symptomatic of cholera. The idea of taking a list of people’s addresses and putting them on a map is what’s called Geocoding. We do that all the time in GIS, and he was doing that in the 1850s.
- Parallel 2:The importance of field validation to address data quality issues.In some places the pattern of the cholera outbreak could only be explained when human behavioural issues were understood. This understanding could only be gained by interviewing local residents.
- Parallel 3:The importance of map quality issues.In some places Dr Snow found that the map he was using was incomplete. Maps that are important to your study results should not be accepted at face value. Accepting “canned” GIS maps at face value is where a lot of GIS users fall over.
- Parallel 4: Dr Snow did Network analysis. By network analysis I mean the google maps functionality that allows you to work out an optimal route between two points on a map.
The second historical GIS study I want to talk about is a 1960s Environmental Planning study by a fellow called Ian McHarg. As with the John Snow example, Ian McHarg developed a spatial technique – GIS is just a tool that made the technique more efficient.
As for the John Snow example where I asked you to look out for the following GIS parallels
- He geocoded the subjects for his study.
- He did field validation to address data quality issues.
- He paid a lot of attention to map quality.
- He did network analysis,
…there’stwo things that I want you to look out for in this study.
- SPATIAL DATABASE CREATION: By this, I mean the attention McHarg paid to bringing a bunch of maps together at the same scale
- MAP OVERLAY:Map Overlay is only possible once a spatial database is in place. If you understand map overlay then you are a long way along the path to understanding GIS. Map overlay is the idea that you can overlay maps onto each other and see different bits of information relating to the same place. It’s used day-to-day in so many organizations these days. At its simplest, someone might overlay property outlines onto an air photo. At its most complex, researchers might relate multiple maps to each other using map weighting or statistical techniques.
In this video I talk about spatial data – points, lines, polylines and polygons. These are the four basic object types in a GIS, and very powerful they are too!
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In the next step we're going to install the free Quantum GIS....
- I’ll talk about why I'm teaching you Quantum GIS and not some other GIS.
- I'll show you how to download it.
- I'll show you how to install it.
- I'll show you how to install the sample datasets.
- We’ll open our first GIS map.