Google Maps: WA housing affordability index

Bankwest has just released a report on housing affordability in WA. Bankwest’s affordability index is a ratio of average house price in a Local Government Area to average worker’s salary. Index values are ranging from 0.9 for Mount Magnet to 49.9 for Peppermint Grove (5 is the upper limit of what is considered “affordable”). The information has been presented in WA Today as an alphabetical list of LGAs with corresponding index value. The paper concluded that workers (defined as a group consisting of police officers, nurses, emergency workers and teachers) “…need to move to Perth’s extremities – or even out of it” to find affordable housing.

This is a good example where information could be presented in a more visually attractive and more informative way – using maps! I have converted Bankwest index table to a thematic map to illustrate how this information could be presented to highlight regions which are still considered affordable.

The key to creating an informative thematic map is to pick the right method for dividing values to be mapped into meaningful categories that convey a certain message. In this case, the story is about locations which are considered affordable. The bank has already defined affordability cut-off value as 5 so that information should be preserved and conveyed on the map. There are many statistical approaches to decide on the split of data to create meaningful categories but on this occasion a simple “rule of thumb” approach is sufficient.

There could be just 2 categories – affordable and non affordable – to convey the message adequately. However, since two-colour map would be quite boring, we could also try to highlight “tail ends” of the data, that is cheap housing areas (eg. those with index value of 2 and below) and those totally out of reach (with index value of 10 and over). The values picked to define the two additional ranges are totally subjective but it does not detract from the key message – that is, which locations have affordable housing.

The selection of colours to present the information on the map is also important. I opted here for a combination to convey the message that there are two categories (affordable and non affordable) but also to indicate grading of index values from “low” to “high”.

Concluding, my appeal is, whenever you think about releasing information relating to postcodes, suburb or other spatially defined regions, please consider putting it also on an interactive map to create a bigger impact! And use my free reference map to enable easy sharing of the information for even greater impact!

Using My Maps for your summer sublet

[Cross-posted from the Google Student Blog]

Today’s guest author is Katie Corner, an Electrical and Computer Engineering student at University of Colorado, Boulder and a Google Student Ambassador. Check out more tips from students on the Google Student Blog, or submit your own to share.

The spring semester ends, and the frenzy begins: Quick, everyone find someone to sublet your apartment for the summer!

Hundreds of students in your university town will be simultaneously advertising their apartments to potential summer subletters. How can you help your apartment stand out among the crowd? Bring in Google Maps to save the day. Google Maps has a feature known as My Maps, which enables you to quickly and easily build a personalized map highlighting the locations you care about — all on one map! Simply share the map link with your family or friends to let them see it too.

Everyone knows that when looking for a summer sublet, it’s all about location, location, location. Where are the closest grocery stores? What’s fun to do nearby? There’s a running path along the creek just two blocks away? And the local bus picks up on the corner? Nothing sells these points better than an easy, personalized map.

It only takes minutes to create your own My Map. To start, sign in to your Google account and go to Click on the link in the upper-left corner labeled “My Maps.” By clicking the “Create new map” link, you can pick a title and get to building your housing map.

To start finding locations of interest and placing them on your new My Map, search for those places in Google Maps, for example “park in boulder co.” After finding the location you are interested in, simply click on the red pin on the map, followed by the “Save to…” link. From here you can easily select the new My Map you created.

After adding a number of specific locations to your map, you can also customize and edit the map to fit your style preferences. To access your map thus far, click on the “My Maps” link in the top left corner of the page, and select the map you are interested in editing. By clicking the “Edit” button, you are now in editing mode on the map and can easily make changes to the names of locations or the style of icon. To make a change to a specific place, just click on that location. On the map, an editable box appears where you can easily make changes, such adding as some notes about the place.

The end product is a unique map showcasing why your sublet is the right option to pick. Here’s an example I used for an apartment in Boulder, Colorado.

Stand out in your next apartment rental posting with My Maps today!

Australian Postcodes User Guide

There is a significant level of interest in postcodes as a convenient reference to locations because of perceived ease of linking them to information about individuals and businesses alike. Over the years postcodes have been put to a wide range of uses in analysing and publishing social trends and population statistics as well as in defining sales, service, franchise or dealership areas. Unfortunately, a misunderstanding of what postcode really is, resulting from a widely held belief about its value as a uniform referencing system, can cause many troubles for the unwary users. This article is a guide for all potential users of postcode boundary data.

Postcode Basics

Firstly, some facts about postcodes, from Australia Post site:

  • Postcodes were introduced in 1967 to facilitate the efficient processing and delivery of mail to customers.
  • Postcodes are only allocated to localities officially gazetted by State land agencies (usually, a postcode covers an area comprising of more than one locality).
  • The decision as to whether a new postcode or an existing postcode is to be allocated to a locality is based on operational efficiency.
  • Because the adoption of new or changed postcodes by customers is slow, changes are only made where significant reasons for change are established. A postcode change will only be considered if such a change leads to either enhanced service to Australia Post customers or operational efficiency to the organisation. Any such change will involve consultation with the local council/shire and residents.

Please note, the above holds true most of the time… but there are exceptions. It is also important to note that there are 3 types of postcodes: delivery areas, post office boxes and large volume receiver. Only delivery areas have meaningful reference to locations “on the ground”.

Sources of Postcode Information

Australia Post publishes a list of all postcodes from its database as a comma delimited text file. The list is updated every month and can be downloaded for free from Australia Post website.

Australian Bureau of Statistics publishes in 5 year intervals a set of Postal Area boundaries that are compiled using outlines of Census Collection Districts. They approximate official Australia Post postcode coverage areas at the time of publishing. These boundaries are available for free download in a range of popular GIS data formats. The next update of the data will be released in December 2010.

A number of private companies also produce and regularly update their own versions of postcode boundaries which are available for purchase. The two major suppliers include MapData Sciences (currently ESRI Australia) and Pitney Bowes (formerly MapInfo Australia). There is also a number of smaller operators that may be a source of free or inexpensive information on postcodes, such as which genaralises and converts ABS postcode boundaries to KML format for use with Google Map and Google Earth and supplies large format static maps in PDF format for printing. Other small suppliers with a variety of postcode related products and maps include:,, and

Common Problems with Postcodes

1. Changing Postcodes
Postcodes are changing over time due to evolving operational requirements of Australia Post. Changes include additions of new postcode numbers and deletions of old ones from the list as well as adjustments to composition of postcodes by adding or removing localities. This is especially the case with new, dynamically growing areas as well as some rural locations and is less of the issue for established metropolitan areas.

It means that postcodes are not a stable spatial reference. It is ok to use them as a snapshot of a particular point in time, but what often happens is that the attribution to “what area constituted that postcode X years ago” is lost from the supporting documentation and important facts can be misinterpreted by future users of the information.

This is a real problem for researchers of social trends – those who insist on using postcodes as the main location reference. As well, it may cause some legal headaches if postcodes are referenced in contracts for supply of services or franchise areas, etc. Postcodes were never meant to be used in this fashion!

2. Changing definitions of localities
On top of changes that are undertaken from time to time by Australia Post, there are also changes to boundaries defining localities which are implemented by State and local authorities. What was locality X in 2007 may now be split into locality X and Y. As the result, it is very difficult to maintain timely and consistent reference of postcode numbers to “what is actually on the ground”.

3. Imperfect procedures of referencing postcodes to localities
Where possible, Australia Post references postcodes to officially gazetted localities but localities are determined by State land agencies and boundaries are recommended by local councils. This process is not coordinated from end to end and sometimes it gets out of sync. Take for example postcode 3478 in Victoria. Australia Post lists Medlyn as a locality included in this postcode (June 2010 edition) yet this locality is not on Victoria’s register of gazetted locations. Referencing postcode numbers to localities is not a science and there can be inconsistencies.


If you must use postcodes, please consider the limitations outlined earlier as well as the following recommendations to avoid potential problems:

If you intend to match postcodes to official ABS statistics:

  • Your only choice is ABS version of postcodes as it will ensure consistency of definitions (that is, postcode X in the data table will correspond to postcode X depicted as an outline on the map). It is particularly relevant for Census of Population and Housing data.
  • If you need to combine those statistics with your own data (eg. client records), geocode individual addresses and then reference them to specific postcode boundaries (eg. using GIS software with “intersect” function capabilities) rather than just rely on postcode component of the address to match the records to boundaries. It is the only way to ensure a particular address/location is part of that specific postcode area.

If you intend to use postcode outlines to define custom areas:

  • Again, ABS version of postcodes is the most cost effective option as it is a free dataset.
  • Define your custom areas once and put effort in maintenance of that dataset over time. You can adjust a composition of custom areas if required (eg. add/ subtract postcodes or even adjust boundaries – but only if topological consistency can be maintained – that is, if changes to the boundary of one polygon can be reflected in the adjoining polygons).
  • It is important to acknowledge that this dataset becomes de facto your own version and that compatibility with “source” postcodes and/ or statistics published on postal area basis may be lost over time.
  • Always reference version of postcodes used in any legal documents to avoid future ambiguity as to what constituted “that” postcode at “this” particular point in time.
  • As in the previous case, if you need to reference those postcode outlines to your own data, run geocoding and then reference individual records to specific boundaries and do not rely on postcode details in the address record alone to match data with boundaries.

If you are relying on postcode boundaries from commercial operators:

  • There is really no point in aiming to always have “the latest” version of boundaries representing postcodes. After all, these are not compatible with ABS statistics (unless the company can assure they reprocess those stats “somehow” to a new representation of boundaries) and besides, what is the benefit of constantly having to reprocess your own data to accurately reference it to the ever changing representation of postcode boundaries? The only exception would be if the company supplies some other unique data that is available exclusively with their proprietary version of boundaries.
  • Although companies claim to have “the latest”, these data are rarely updated on continuous basis (ie. every month), rather in 3 or 6 monthly intervals so, you are still getting “dated” product.
  • Don’t assume you will be able to reference your address records to “the latest boundaries” using only postcode number unless your address details and postcode boundaries refer to the same time period. In most cases they don’t and you cannot avoid geocoding and then running GIS “intersect” processing of data to ensure reliability of information.

In conclusion, although postcodes appear to be well recognised spatial units for referencing locations, the complexity associated with accurate delineation of postal boundaries greatly diminishes their usefulness. If you can, avoid using postcodes! If you can’t, be aware of all the limitations, especially when drawing conclusions with far reaching consequences.