Quantum GIS tutorial

GIS CHALLENGE_3-sandys version of header

Announcing the “QGIS for Newbies” Quantum GIS Tutorial

The Challenge… Shade a GIS Map in 5 Steps

You’ll learn…

* What is a GIS
* How to download and install QGIS.
* How to open GIS air photos and maps in QGIS.
* How to zoom in and out, query, measure…
* How to interpret a GIS map.
* How to create your first shaded map, step-by-step.

and more…

* 3 hours of subtitled video
* Video transcripts
* Study notes
* Sample dataset

Read the rest of this entry »

Using Remote Sensing for Arctic and Antarctic Sea Ice Change Detection

Using 25km daily remote sensing grid cell data from a satellite mounted microwave sensor, National Snow and Ice Data Centre (NSIDC) scientists have shown that the minimum extent of Arctic summer sea ice is almost half that detected in the late 1970s.

As with any remote sensed data, the NSIDC tempered their interpretation with both an understanding of the sensor’s limitations, and the nature of the Sea Ice itself. In this case, they understood that error could be introduced by motion, weather and surface effects, so a cell was only flagged as having sea ice if it was detected there on multiple days. Read the rest of this entry »

How important is the scale of a map?

A scalebar is not the only thing that indicates the scale of a mapBy
What determines the scale of a map ? I was just reading a great post about cartographic scale from the National Geographic site and thought I’d write a short post about it myself. The article makes the point that as the scale of a map changes then the cartographer is faced with choices. When producing smaller scale maps (think ship in bottle) that cover large areas, map making becomes particularly difficult because things need to be left out. But on what basis does the cartographer make these choices? Usually it is with the “audience” in mind – walking maps will highlight features important to walkers, while street maps will highlight features important to road users. This all makes sense.

But what happens to the scale of a map when it finds its way into a Geographical Information System? More often than not the cartographer’s art gets lost and maps find themselves being used for purposes and at scales other than those they were intended for. In some circumstances this can lead to bad outcomes for inexperienced map users.

All maps are simplifications (models) of reality and how much information is contained in them depends on the scale of the map. On a paper map…

  • a scale of 1:10,000 means that one length of measurement equals ten thousand in real life.
  • A 1:250,000 (small) scale map will contain less information than a 1:10,000 (large) scale map, and boundaries usually have less detail.

It is important to understand that cartographers create maps with a scale of printing and interpretation in mind. The scale of a map relates very closely to the amount of time and effort that went into producing it. A map produced on the basis of a week of field work will be of a poor quality compared to one that took a year of fieldwork over the same area. A mistake that people sometimes make is to enlarge a map on a photocopier in the hope of producing more detailed mapping. Sometimes its OK to do this, but increased size does not equate to increased detail – no matter how many times you enlarge a world atlas on a photocopier, local streets don’t appear!

An understanding of scale is an important thing for a GIS analyst to have because many GIS maps have their origins in old paper maps. During the 1990s governments around the world put much effort into building their digital map infrastructure, and their paper map archives were converted (digitized) into maps that could be used in GIS software. However, in a GIS the cartographic “tells” of scale that existed on the original paper map (thick lines, scalebars, etc.) disappear, so the map effectively becomes scaleless.

For maps that are surveyed such as land ownership (cadastre) and roads, this issue is less important than for maps that are interpreted (ie. environmental themes and social surveys).

The take-home message is that whenever possible, the maps you use for your projects should be at an appropriate scale for the project’s purpose. Because the scale of a map relates to the scale of its collection, and not the scale of its display, whenever appropriate, on your printouts you should indicate the scale of the original mapping as well as your GIS’s auto-generated scale bar.

The theme of Traps with Maps is a thread that runs throughout my 7 Day Home Study GIS course. The course uses the free Quantum GIS to teach you how to get your own GIS project running on your desktop. Check out the details of the course here.


Where Scale Permits http://t.co/fkz27xQz

What are the careers in Geography

What are the careers in geography? GIS analysis of the census is an important one.What are the careers in geography? Well GIS analysis of the census is an important one!

In many countries around the world 2010 and 2011 were big years for the national statistics bureaus – these were National Census years. Censuses date back to biblical times. A big reason for them has always been the need to understand how many people should be paying taxes and how much! These days the reasons are a little more sophisticated. Mostly censuses provide information to help governments plan where to build services such as schools and hospitals, and how to do the best job of formulating strategic plans and policies.

In my mind, one of the most exciting features of census data is the ability to undertake time series analysis. Knowing the total population of a country is one thing, but knowing that the population has increased or decreased since the last census is a different thing again. GIS professionals become useful here because a further vital piece of information in this puzzle is “where” population has changed. Notice I use the word “changed” Read the rest of this entry »

Maps that Lie! A HIV-AIDS example


In this post use the AIDSvu website to I talk about maps that lie. The post is in two parts written about a week apart. Be sure to read both parts and watch the video. Yes, even I can be wrong! Read on…


AIDSvu.org has a web application that allows you to view aids information for the United States on a map. It’s a fantastic tool for public education and awareness, particularly because one in five people who are HIV positive are unaware of it.

The AIDSvu tool allows mapping at State and County scales according to themes such as ethnicity, sex and age. This is a fine example of public-access GIS. However, you need to be careful when comparing the maps. Although they are comparable with each other insofar as they depict infection rates per 100,000 people, as is the case with mapping projects such as this, the color scheme of the maps is misleading. Let’s explore this issue a little.

When looking at the thumbnail images it would appear that the AIDS rate in Detroit and Washington DC are similar. After all, both cities have areas shaded yellow (least cases per 100,000) and dark purple (most cases per 100,000). However, when we look at the individual maps we see that they should not be compared because areas shaded purple in the Detroit map (654+ cases per 100,000) are not comparable to a purple class, but rather a yellow class (440-670 cases per 100,000) in the Washington DC map.

Now read the captions in the maps below…

Maps that lie

A cursory look at these two maps would make you think that the incidence of AIDS in some areas of Detroit and Washington DC was similar. However, a close comparison of the two reveals something quite different. Read on…


Maps that lie

The purple legend category in this map (most cases per 100,000) cannot be directly compared to the purple legend category in the Washington DC map. The purple class here is equal to a yellow class in the Washington DC map.


Maps that lie

In this map the purple category represents a 6 fold+ greater incidence of AIDS than Detroit.


The lesson: Always look closely at a GIS map’s legend, particularly when you are comparing maps to each other. Just because they look the same it doesn’t mean that they are!

PART 2 – the “lesson” continues.

While I was making the YouTube video I noticed that I got the first part of this post a bit wrong. You see, it turns out that I was comparing the “Rates per 100,000 theme at Census Tract scale” in Washington DC to the “Cases theme at ZIP Code Scale” in Detroit. Look closely at the screen captures above and see for yourself. Comparing Rates to Cases, or ZIP Codes to Census Tracts would be akin to comparing apples to oranges. My goodness, I don’t know if there’s a term to describe my error in incorrectly comparing both THEME and SCALE!  At least my final comment in part 1 of this post that its important to look closely at a map’s legend was on target!!!

 Don’t forget to signup for my free eCourse “Quantum GIS for Newbies”. The link is just to the right ->.

What is a GIS map

What is a GIS MAP? Its a map in a coordinate system and has a database that stores information about its features

A GIS map contains points, lines and polygons

What is a GIS map? Its a digital map that has two important features…

  1. Coordinate system: A GIS map is a computerized map that’s in a coordinate system. This allows it to be related to other GIS maps, and contrasts to a computer graphics map, the features in which can only be related to other features in the same map.
  2. Database: Each feature in a GIS map has a database entry describing it. This means that information about a map feature can be stored, and custom maps produced based on the information in the database. Consider for example, a power pole. It  might be made of wood, might have been installed on a particular date and might carry high voltage wiring. A GIS professional could produce a map “all wooden power poles installed during the winter months” by using a database query.

These two features of GIS maps mean that maps from many different sources can be related to each other and analyzed, rather than just looked at.

A GIS map has three deceptively simple categories of map features – points, lines and polygons (areas).

Table 1 –  What is a GIS map?: Having this map as a GIS map may seem an overkill for the types of questions I suggest it would be allowed to be answered, but imagine how useful a GIS map would be if you needed to answer these questions for an entire country!

Map feature

Paper map

GIS map

Points You can see a school the map You can find out how many schools are on the map?
Lines You can see roads and streets You can find out the length of all roads on the map?
Polygons (Areas) You can see a park You can find out how big the parks are?

Don’t forget to signup for my free eCourse “Quantum GIS for Newbies”. The link is just to the right ->.

Roadless as a conservation measure

Recently, Google was approached by Kriton Arsenis, a Member of the European Parliament and its rapporteur on forests. He made the point that keeping an area roadless means that a territory is shielded against deforestation pressures. This provided an incentive for Google to investigate, and by buffering their road map by 10 km, Google was able to create a map of areas less subject to deforestation pressures. Google quite rightly has a number of caveats with the map, and does point out that its MapMaker product can be used to notify Google of incorrect data.

Projects like this highlight both the strengths and weaknesses of GIS. On the one hand they can inspire people to think differently about problems, but on the other, in the hands of the lazy, such maps can be promoted as being correct.

This big flaw with this type of project is that the roads in those areas most subject to conservation pressures are generally the least likely to be mapped.  I find it difficult to imagine companies undertaking illegal logging being interested in notifying anyone about their illegal roads. Aside from that, many counties mapping agencies are underfunded, and lack the internet infrastructure that would allow the use of products like Google MapMaker.

So, hats-off to Google for undertaking this project, but at the same time, a lesson for all of us to heed.

The full article can be seen at http://google-latlong.blogspot.com.au/2012/06/where-roads-arent-and-why-it-matters.html

Don’t forget to download my free eBook “10 Practical Applications Of Geographical Information Systems”. The link is just to the right ->.

Public Health Map Used To Stem Cholera Outbreak



In this What Is GIS episode I want to talk about public health mapping using John Snow’s classic mid 19th century cholera mapping exercise. It’s a fascinating story about a 19th century doctor, a public health map and a pump handle. Dr John Snow is an important person in the history of geography. The mapping he undertook inspired a way of thinking that led to the Geographical Information Systems we have today. What’s important about this example is that it illustrates that a purely GIS technology solution would be unlikely to have yielded a result as convincing as one where the person doing the mapping dons their boots and makes an effort to investigate and explain away anomalies in their mapping. John Snow understood the problem he was mapping and that made a huge difference to the usefulness of his results. Read the rest of this entry »

How to overlay maps

How to overlay mapsIn the video I demonstrate one of the earliest examples of the strategic use of map overlay in planning. I tell the very beginning of the story of how to overlay maps. If you understand map overlay then you are a long way along the path to understanding GIS.

There are a few people in the history of geography who laid the foundations for the Geographical Information Systems that we have today. They developed the techniques and GIS is a tool that makes them more efficient. One of the primary functions of any GIS is map overlay – the ability to overlay multiple maps onto each other so that new understanding of an area can be gained based on the relationship between the maps. A fellow called Ian McHarg deserves the most credit for the development of this technique. Although geographers at the time, poo-poo’d his techniques as being nothing new, because, of course, they had been overlaying maps forever, Ian McHarg was the first to consistently make the effort to pull all the information together in a way that they could be related to each other.

Ian McHarg wrote a book about this called “Design With Nature”. This is the least textbook-like of all the textbooks I have ever read. In fact, I’d go so far to say that contains prose moreso than text! McHarg’s story is one of a joyful childhood living equal distance from the city and country, the hideousness of WWII and his subsequent return to bulldozed memories. WWII left him with tuberculosis and his recovery from this began in a miserable dank filthy repatriation centre in Scotland, and ended with an opposing experience in a Swiss sanatorium surrounded by countryside and mountains. He sees the link between health, happiness and environment, and concludes that we need, not only a better view of man and nature, but a working method by which the least of us can ensure that the product of his works is not more despoliation (p.5).


Ian McHarg, 1967, Design With Nature, John Wiley and Sons

Don’t forget to signup for my free eCourse “Quantum GIS for Newbies”. The link is just to the right ->.

Mapping Links Pollution to Regulation

Time series GIS mapping of a 25 year study of acid rain frequency and intensity in the United States shows a decrease over time. Read the rest of this entry »

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