My home city of Adelaide has many of its main roads laid out in regular grids, unlike topographically constrained cities like Sydney and Brisbane.

This article is viewable both on this site and on Mappage, my webapp for looking at statistics. If you’re reading this on a large screen, it’s best to read this article in Mappage, where I have set it up with maps. Unlike many of my articles that use Mappage, this one is all maps and no statistics.

This article is viewable both on this page and in plain form on the Mappage WordPress site. Clicking the M links here will show things on the map. This is not so much an article with a few visualisations embedded; it is my statistics & mapping web app (called Mappage), which I have set up to accommodate articles like this. Unlike many of my articles that use Mappage, this one is all maps and no statistics.

Australia changed to metric in the 1970s (w), so while my generation has always used kilometres, Adelaide was planned when distances were measured in miles (1.61km).

Starting in the **CBD** M0 with the most familiar grid, people used to speak of a square mile, so you’d think that if East Tc were brought into line (ie Hutt St), the four terraces of the CBD would form a square with sides of a mile. A close look shows that it isn’t square. It is one mile from North to South; this is divided neatly into ten by the main streets. But from West Tc to Hutt St is 1⅓ miles, and to the furthest part of East Tc is 1⅔ miles. It’s a mile from West Tc to Pulteney St, Morphett St to Hutt St or King William St to East Tc. Victoria Sq is exactly 138.6°E. The latitude is not a round number but presumably was chosen to put North Tc close to the slope down towards the river.

There’s something of a grid covering the **middle half** of Adelaide M1. It’s seen most clearly in just south of Cross Rd and Anzac Hwy. The main roads that run N-S are spaced a mile apart (actually more like 1.63km). All the way from Brighton Rd & Tapleys Hill Rd to Stradbroke Rd, 9 miles from west to east. This grid covers most of the Adelaide plain south of Grand Junction Rd. Note that this includes the CBD with West Tc and Pulteney St. Many Adelaide suburbs are half a mile wide following this grid. Frederick Rd is half a mile west of Tapleys Hill Rd^{1}A whole mile wouldn’t work; West Lakes used to be swamp. Frederick Rd was the boundary of the former Henley & Grange LGA, hence the odd-looking LGA boundary through West Beach in line with Frederick Rd.. The roads running W-E don’t have many round miles: There’s one mile from Trimmer Parade to Grange Rd, along with North to South Tc as mentioned above. We’ll come back to them later.

The **Onkaparinga** grid M2 is another obvious one. From Happy Valley to Sellicks Hill, many main roads follow grid lines. The spacing is 1.1 to 1.2 km, which occurs in other grids as well. Why was this distance used? It’s more than two thirds of a mile so doesn’t seem to be any round number. I’ve never read anything about this so I guessed it was the square root of a half of a mile (1.138km). The area of one of these squares would therefore be half a square mile and the diagonal across one mile. But in drawing up the Onkaparinga grid, I found 1.165km matched better^{2}Using the overestimate of a mile only makes up half the difference. I don’t know why this distance was used. 12 of these units from Rowley Rd to Education Rd. From Woodend Rd & Kenihans Rd to Gulf View Rd is 24 units.

You would have noticed that these Adelaide grids are not exactly aligned with compass directions, in fact it’s about 3.4° out^{3}Gepps Cross is true north of Victoria Sq, while Main North Rd is collinear with Pulteney St. ⅓mi across in 9km.. Again I don’t know why. The Australian Map Grid for the Adelaide area is tilted the other way, so on maps using AMG (such as UBD street directories) the Adelaide grid will be at ~5°. But now we move to some grids that are on different angles entirely.

The **Salisbury** area has a similar grid M3 to Onkaparinga, but at an angle of 36.5° from true, or 40° from the other grids. For the roads running SW-NE, it’s 7 units from Bridge Rd to a section of Heaslip Rd. In the other direction, 6 units from Saints Rd to Globe Derby Dr (plus an extra 80m between Kings Rd and Shepherdson Rd). The suburbs of Brahma Lodge and Salisbury Plain are single squares of this grid (half a square mile). I haven’t looked at historical maps, but I’m guessing Main North Rd was there first and the grid followed.

The **Playford** grid M4 is tilted 27.7° from true, or 8.8° from the Salisbury grid, possibly following the existing direction of Main North Rd for that section. From Judd Rd to Curtis Rd & Craigmore Rd is 5 units. The grid stretches 10 units from Gawler Rd to Main North Rd & Philip Hwy with a further unit to Bentley Rd & part of Midway Rd, or 1.5 units to Adams Rd & (less accurately) Blackburn Rd^{4}And a walking track! This line, unremarkable on a road map, is one of the major demographic dividers in Adelaide with three Elizabeth area suburbs on one side and Hillbank & Craigmore on the other..

There’s a bit of a grid in the **Tea Tree Gully** area M5, but this time halves of units are added in. Grand Junction Rd to Greenwith Rd is 5.5 units. Nelson Rd to Haines Rd is also 5.5 units. Reservoir Rd lines up with Stradbroke Rd, which allows us to connect this grid to the middle half.

Returning now to that **middle half** M6, what about the roads running W-E? There are roads from Montacute Rd to Sturt Rd spaced 2.73km apart. This spacing was in use by 1838 with many sections being a quarter of this by half a mile (eg Beulah Park). Again it doesn’t seem to be a round fraction of a mile. It’s close to the square root of 3 miles (2.79km), which would make the diagonal across one of these blocks would be two miles, so equilateral triangles with sides of 2 miles could be drawn from the main intersections, but for all that follows, a ‘unit’ refers to 2.73km. Again I don’t know why this length was used.

Gorge Rd is half a unit north of Montacute Rd, Lyons Rd to Grand Junction Rd is the same distance, but Gorge to Lyons is an unremarkable 2.1km. Grand Junction Rd to Muller Rd is 1 unit, a touch more to Regency Rd, and just over 1 more to Fitzroy Tc. Seacombe Rd is just short of half a unit south of Sturt Rd. Kensington Rd, part of Adelaide’s x-axis, divides a unit in half, as do Ridley Gr, Hallett Ave, Glenunga Ave, Raglan Ave & Bray St. It’s nearly 3 units from Grand Junction Rd to North Tc.

Together M7 the grids cover most of the flatter parts of Adelaide. Knowing about them meant I could sometimes, while riding my bike, estimate the distance to my destination. I didn’t realise it was as extensive as it was; the outer two grids I had named Noarlunga and Elizabeth before realising how far out of suburbia they stretch. I’ll update this if I hear of any explanations for the distances and angles.