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Knowledge base

Putting road condition on a map

A spreadsheet of segment scores is a correct answer to a question nobody in the room is asking. The question is "which roads", and that is spatial.

Most councils hold their road condition as rows: a segment identifier, a chainage, a score, a date. It is the right structure for calculation and the wrong one for a decision made by a group of people, because nobody in a council chamber thinks in chainages. They think in the road past the school and the one the trucks use.

Moving the same data onto a map changes three things, and none of them is decoration.

1. The gaps become visible

On a spreadsheet, a missing condition score is a blank cell near the bottom of a column of 900. On a map it is a grey line running through the north of the shire, and the first question anyone asks is "why is that one grey?"

That is the single best argument for mapping. A network summary is only as honest as its treatment of the roads nobody has looked at, and a table hides those beautifully. A map cannot — provided the legend has a row for not surveyed that is visibly different from both good and poor.

If the only way to show an unsurveyed road is to colour it as though it scored zero, the map is worse than the spreadsheet.

The same applies to surface type. 61% of Australian local road length is unsealed — 413,000 km against 265,000 km sealed (ALGA, 2024 National State of the Assets). A map that colours gravel roads on a sealed-road scale is showing a score that was never valid for them, across the majority of the network.

2. Patterns appear that no sort order would find

Deterioration is not randomly distributed. It follows drainage, soil, haulage routes, the age of a subdivision, the year a contractor sealed a batch of streets. Those patterns are spatial by nature, and a column sorted by score cannot surface any of them — the roads that share a cause are scattered through the list.

Seeing five poor segments that happen to sit along one creek line is the beginning of a different conversation from seeing five poor segments ranked 14th to 31st.

3. The conversation changes shape

A councillor shown a ranked list argues about the ranking. A councillor shown a map argues about the roads — which is the argument you actually want, because it is the one where evidence helps.

It also makes a particular objection answerable on the spot. "Why isn't my street on the list?" is hard to answer from a table and easy to answer from a map with the street's own score, its survey date and the treatment it would need one click away.

What makes a condition map usable rather than pretty

Four things, in rough order of how often they are got wrong:

A legend that includes the unknown. Good, fair, poor — and not surveyed, in a colour that reads as absence rather than as a grade. Grey, usually. This is the one that gets dropped.

Colour that survives being printed in black and white, because the map will end up in a committee paper. Distinguishable by lightness, not only by hue.

A date on the face of it. Condition is a measurement with a shelf life. A map with no as-at date invites a reader to assume it is current, and in two years it will not be.

Click-through to the evidence. The map is a way in, not an answer. A segment should open onto what was seen, when, by which method, and what the score was built from. Without that the map is a picture, and a picture is not something anyone can check.

The thing a map cannot do

It cannot rank. A map shows you where the poor roads are; it does not tell you which to do first, because that depends on cost, on what the treatment achieves, on traffic, and on what else is competing for the same budget. Those are table questions.

The useful arrangement is both, pointing at each other: the map for which roads and where, the ranked programme for in what order and at what cost, and a way to get from one to the other without re-querying anything.

How PaveKeep handles this

PaveKeep puts the whole network on a map, coloured by condition, with a legend that includes roads nobody has surveyed — and those report as unknown rather than as zero, which is the point the rest of the product turns on. Open any segment and it says what was seen, when, and by which method, with the arithmetic behind the score.

The network also exports in a standard mapping format, so it opens in whatever GIS the council already runs. Nothing is locked in.

PaveKeep is built for small and regional councils and is not yet in use at any council.

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