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About ARIA+ (Accessibility/Remoteness Index of Australia).

ARIA+ is widely accepted as Australia's most authoritative geographic measure of  remoteness.

ARIA and it's successors ARIA+ and ARIA++, are indexes of remoteness derived from measures of road distance between populated localities and service centres. These road distance measures are then used to generate a remoteness score for any location in Australia.

ARIA+ is the standard Australian Bureau of Statistics (ABS) endorsed measure of remoteness.  ARIA+ forms the basis for the ABS' "Remoteness Structure" component of the Australian Standard Geographical Classification.

Summary

ARIA+, like its predecessor ARIA, is an unambiguously geographical approach to defining remoteness.  ARIA+ is a continuous varying index with values ranging from 0 (high accessibility) to 15 (high remoteness), and is based on road distance measurements from 11,879 populated localities to the nearest service centres in five size categories based on population size. The five distance measurements, one to each level of service centre, are recorded for each populated locality and standardized to a ratio by dividing by the Australian mean for that category. After applying a threshold of three to each of the ratios are summed to produce the ARIA+ score for each populated locality across Australia. An interpolation procedure was used to interpolate the index values for each of the localities to a 1 km grid so that all areas of Australia recorded an index value. Using the interpolated grid surface scores for larger areas such as CDs and SLAs were derived.

The major advantages of ARIA over other methods of measuring remoteness are that;

As a comparable index of remoteness that covers the whole of Australia, ARIA+ provides a measure of remoteness that is suitable for a broad range of applications including assisting in service planing, demographic analysis and resource allocation.

Although ARIA+ provides a measure of accessibility and remoteness for the whole of Australia, including metropolitan and non-metropolitan areas, the principal focus of the index has been to quantify accessibility in non-metropolitan Australia. This is not to deny the importance of service access issues within major urban areas, but a detailed analysis of accessibility within urban areas is believed better served by a dedicated methodology. GISCA has recently completed a prototype of a metropolitan accessibility index that has adapted the ARIA methodology and underlying principles to measure accessibility in the urban context.

Further information on the ARIA+ National Data Product.

Click here to view ARIA+ scores online.

Brief Methodology

Terminology

ARIA+ - (Accessibility/Remoteness Index of Australia Plus) measures remoteness in terms of access along the road network from populated localities to each of five categories of service centre. Localities that are more remote have less access to service centres; those that are less remote have greater access to service centres.

Populated Localities - refer to the primary areas being classified. These are based on AUSLIGs (now Geoscience Australia) “Populated Centres” and supplemented with some additional populated towns from the AUSLIG gazetteer and other mapping sources. Localites were only added to the database if they were known to be populated. There are 11,879 populated localities in the ARIA+ database. 

If one thinks of ARIA as based on the distances people have to travel to obtain services, then populated localities are where they are coming from, and service centres are where they are going to.

Service Centres - are populated localities where the population is greater than 1000 persons (greater than 200 in the case of ARIA++).  The Urban Centre/Locality Structure of the 2001ASGC has been used to define the areal extent and population of these areas. The table below shows the population break points that were used to group Urban Centres into the five Service Centre categories. The ARIA+ analysis considers about 730 services centres in determining remoteness values across Australia. These service centres are a subset of the 11,879 populated localities. In instances where the ABS defined Urban Centres are split by a state boarder, such as in the case of Albury and Wodonga, the population and spatial extents for each of these Urban Centres have been combined and treated as one service centre.

Service Centre Category

Urban Centre Population
A
 250,000 persons or more
B
 48,000 – 249,999 persons
C
 18,000 – 47,999 persons
D
 5,000 – 17,999 persons
E
 1,000 – 4,999 persons
F (ARIA++ only)
 200 – 999 persons

Index Derivation

The ARIA+ methodology regards services as concentrated into Service Centers.  Populated localities with populations of greater than 1000 persons are considered to contain at least some basic level of services (for example health, education, or retail), and as such these towns and localities are regarded as Service Centres. Those Service Centres with larger populations are assumed to contain a greater level of service provision.  A total of 738 Service Centres, classified by their population into five categories, were used in the ARIA+ methodology.  

The road distance from each of the 11,879 Populated to the boundary of the nearest Service Centre in each category was calculated.  This calculation resulted in five distance measurements being recorded for each Populated Locality, one for each Service Centre.  Populated towns within a service centre (based on ABS-defined Urban Centre boundaries) in the relevant category were given a distance value of zero for that category.  Each distance value was divided by the Australian average (mean) for that category in order to derive a standardised (or ratio) value. Distance measurements were then standardised so that large distance measurements would not overwhelm the effect of the other distance measurements. 

Each ratio value was thresholded at 3 (i.e. 3 times the Australian mean) to remove the effects of any remaining extreme values from the index.  All towns with a ratio value higher than 3 for a given category were to be considered 'remote' in terms of access to that category, and were given a value for that category equal to the threshold.  For each category, each Populated Locality the standardized value from each of the five classes was summed to produce an overall index value ranging between 0 and 15. The lower the value, the greater the access to services. Following is an example calculation.

Example ARIA+ Calculation

The locality of Pine Creek in the Northern Territory is:

2,847 km from the nearest Category A Service Centre (Adelaide)

226 km from the nearest Category B Service Centre (Darwin)

226 km from the nearest Category C Service Centre (Darwin)*

91 km from the nearest Category D Service Centre (Katherine)         

91 km from the nearest Category E Service Centre (Katherine)**

Divide by national average for each category,

Its Category A score is 2,847 / 415 = 6.86  {exceeds threshold so score = 3.00}
Its Category B score is 226 / 228 = 0.99
Its Category C score is 226 / 133 = 1.69
Its Category D score is 91 / 84 = 1.08
Its Category E score is 91 / 43 = 2.11

And,

Its ARIA score is thus 3.00 + 0.99 + 1.69 + 1.08 + 2.11 = 8.87

* There were no Category C Service Centres closer to Pine Creek than Darwin, so Darwin functions as both the closest Class B and Class C centre.

** There were no Category E Service Centres closer to Pine Creek than Katherine, so Katherine functions as both the closest Class D and Class E centre.

The ARIA+ values for all Populated Localities were then spatially interpolated to form a grid of 1km cells across the whole of Australia.  This grid enabled remoteness to be expressed continuously over the total land area.  In addition, it allows ARIA+ values to be calculated (by summation of 1km grid cells) for any spatial unit, such as Statistical Local Areas, and Census Collection Districts.