QGIS for Beginners #1: QGIS Orientation. +Free eBooks

Link to scale article:   https://gis-university.com/what-determines-the-scale-of-a-map-in-gis/

You will learn: The four types of spatial data in a GIS – points, lines, polylines and polygons. 

They sound simple, but they are very powerful!

You will learn: that although maps can add a wonderful dimension to studies, they should not always be accepted at face-value.

John Snow if often referred to as one of the Fathers of GIS. His 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 water well 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. As you watch the video, look out for four parallels with modern-day GIS...

• Parallel 1 - geocoding: 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 1850's.

• Parallel 2 - field validation: 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 behavioral issues were understood. This understanding could only be gained by interviewing local residents.

• Parallel 3 - map quality issues: 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 - network analysis: 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.

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You will learn: 1) The importance of making the effort to assemble the maps that are important to your study, and 2) the principle of Map Overlay. 

In McHarg is also often referred to as another Father of GIS. We're about to have a look at one of his 1960s Environmental Planning studies. As with the John Snow example, Ian McHarg developed a spatial technique – GIS is just a tool that made the technique more efficient.

In the previous video about Dr John Snow's cholera mapping exercise, I asked you to look out for the following GIS parallels...

• Dr Snow geocoded the subjects for his study.
• Dr Snow did field validation to address data quality issues.
• Dr Snow paid a lot of attention to map quality.
• Dr Snow did network analysis




In the same vane, I want you to look out for two things in this video about Ian McHarg.


1. SPATIAL DATABASE CREATION: By this, I mean the attention that Ian McHarg paid to bringing a bunch of maps together at the same scale

2. 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.

Download the 69 page Environmental Mapping With GIS eBook

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Thankyou so much

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Once you have a dot on a map you can relate that dot to any boundary you want. In this video I turn house sales into GIS dots on maps and relate them to GIS maps of grid squares from a local street directory. 

Point data are very, very flexible!  The types of analysis you can do using point data are only limited by your imagination. 

To get a point on a map you must geocode it. That is to say, convert your geocode (in this case address) into a GIS dot by relating it to a GIS map that has an address with the exact same address details in it. 

In this example I compare one real estate agent’s house sales in an area to a database of all house sales to analyse their share of sales. Market share is the number of houses sold by a real estate agent within an area, compared to all the sales made by all agents in the same area.  So, if 10 sales were made in an area and five of those were made by our real-estate agent, then our agent will have a 50% market share. Another measure of market share could have been an agent’s share of the total dollar value of sales.

This GIS project involved analysing all the house sales made by one real estate agent in 1991 and 1996.  First I geocoded all the sales made by the Hocking Stuart real estate agent (realtor) and then I geocoded all property sales for metropolitan Melbourne. Both point datasets were then related to a GIS grid of a local road atlas.

The resulting time series maps showed that the Hocking Stuart real-estate agent had expanded over a five year period and while it was expanding it lost market share on the home front.  It’s very important when you look at data such as these to think behind the scenes. 

• Inner city house values (and sales commissions) are far greater than those in the outer suburbs.  So a loss of market share in the inner city may have a far greater impact on the bottom line then again in markets year on the periphery.
• Some gains in market share might be from a low number of sales. A change in market share for a grid with a few sales of low value had a different meaning to the agent than a change in a grid that has lots of high value sales.

PS. The examples were from days prior to QGIS being as stable and usable as it is today so I used MapInfo to produce these maps. That said, nowadays, the maps in the video could easily be produced using QGIS!