Proposal:OpenInfraMap tower icon scaling by voltage
| OpenInfraMap tower icon scaling by voltage | |
|---|---|
| Proposal status: | Draft (under way) |
| Proposed by: | GlavkomLVO |
| Tagging: | power=tower
|
| Applies to: | node |
| Definition: | Scale OpenInfraMap power=tower icons according to the nominal voltage of the associated power line |
| Statistics: |
|
| Rendered as: | Tower icons would use different sizes depending on voltage |
| Draft started: | |
| Proposed on: | 2026-08-30 |
Summary
This proposal suggests scaling the rendered icon for power=tower in OpenInfraMap according to the nominal voltage of the power line associated with the tower.
The aim is to provide a subtle visual hierarchy between towers belonging to lower-voltage, high-voltage, EHV and UHV networks while preserving the existing tower symbol and avoiding excessive map clutter.
This proposal concerns OpenInfraMap rendering only. It does not propose any change to OpenStreetMap tagging.
No new tags are introduced and the meaning of power=tower, power=line, voltage=* or any other OpenStreetMap tag would be changed.
Rationale
At present, power=tower is generally displayed with approximately the same symbol size regardless of the voltage of the line carried by the tower.
This means that, from a cartographic perspective, a tower on a relatively low-voltage line may have approximately the same visual prominence as a tower belonging to a 500 kV, 750 kV or 1000 kV transmission network.
Transmission towers used for higher-voltage lines are often physically larger because of increased electrical clearances, conductor arrangements and mechanical requirements. However, voltage alone cannot determine the actual physical dimensions of an individual tower.
For this reason, this proposal does not attempt to represent the physical dimensions of towers literally.
Instead, the icon scaling is intended to create a modest cartographic hierarchy.
At the lower end, a tower icon rendered at approximately 60% of the current reference size has a visual footprint similar to the existing power=pole symbol.
This provides a useful baseline while still keeping towers and poles visually distinguishable by their different symbols.
Proposed rendering
The following voltage classes are proposed:
| Nominal voltage | Tower icon scale | Typical examples |
|---|---|---|
| Unknown / unavailable | 60% | — |
| ≤ 69 kV | 60% | 10, 20, 35, 66, 69 kV |
| 70–199 kV | 70% | 110, 115, 132, 138, 150 kV |
| 200–399 kV | 80% | 220, 230, 275, 330, 345, 380 kV |
| 400–599 kV | 90% | 400, 420, 500 kV |
| 600–899 kV | 100% | 735, 750, 765 kV |
| ≥ 900 kV | 110% | 1000, 1100, 1150 kV |
The percentages are relative to the reference tower icon size.
The 600–899 kV class is used as the 100% reference size. This includes common EHV systems such as 735 kV, 750 kV and 765 kV.
The proposed scale therefore follows a simple visual sequence:
60% → 70% → 80% → 90% → 100% → 110%
Reference voltage levels
For commonly encountered transmission voltage levels, the proposal can be summarised as follows:
| Voltage | Tower icon scale |
|---|---|
| 35 kV | 60% |
| 110 kV | 70% |
| 220 kV | 80% |
| 330 kV | 80% |
| 400 kV | 90% |
| 500 kV | 90% |
| 750 kV | 100% |
| 1000 kV | 110% |
These are examples of the voltage ranges above rather than a requirement for exact voltage matching.
For example:
- 132 kV would use 70%
- 230 kV would use 80%
- 275 kV would use 80%
- 345 kV would use 80%
- 420 kV would use 90%
- 735 kV would use 100%
- 765 kV would use 100%
- 1150 kV would use 110%
Voltage determination
The renderer should preferably determine the scale from the nominal voltage of the power=line associated with the tower.
A conceptual implementation would be:
power=tower
|
+-- determine associated line voltage
|
+-- unknown -> 0.60
+-- <= 69 kV -> 0.60
+-- 70-199 kV -> 0.70
+-- 200-399 kV -> 0.80
+-- 400-599 kV -> 0.90
+-- 600-899 kV -> 1.00
+-- >= 900 kV -> 1.10
Discrete voltage classes are preferred over continuous interpolation.
Transmission systems normally use standard nominal voltage levels, and very small differences in icon size would provide little useful information at normal map zoom levels.
For example, there is little cartographic benefit in rendering a 275 kV tower slightly smaller than a 330 kV tower, or a 735 kV tower slightly smaller than a 750 kV tower.
Broad voltage classes therefore produce a simpler and more predictable hierarchy.
Towers with unknown voltage
If no usable voltage can be determined, the tower should use the 60% scale.
Rendering unknown-voltage towers at 100% would give them approximately the same visual weight as known 735–765 kV infrastructure even though no voltage information is available to justify this.
Using the smallest class as the fallback keeps the object visible while avoiding an unsupported EHV-like prominence.
Thus:
unknown voltage -> 0.60
rather than:
unknown voltage -> 1.00
Towers carrying multiple voltage levels
Where a tower carries circuits of more than one nominal voltage, the highest associated voltage may be used to determine the icon size.
For example:
voltage=220000;110000
would use:
scale = 0.80
and:
voltage=500000;220000
would use:
scale = 0.90
Using the highest voltage is intended as a simple rendering rule only.
It does not imply that the highest-voltage circuit completely describes the physical dimensions or design of the tower.
power=pole
No corresponding scaling change is proposed for power=pole.
The existing pole symbol should remain unchanged.
The 60% scale for the smallest tower class was selected partly because it gives a low-voltage tower approximately the same visual footprint as the existing pole icon.
The distinction between the two objects remains visible through symbol shape:
Therefore, voltage-dependent scaling does not require enlarging or reducing the pole symbol.
Examples across different power systems
The proposed ranges are intended to accommodate common nominal voltage levels used in different countries.
| Nominal voltage | Proposed scale |
|---|---|
| 35 kV | 60% |
| 66 kV | 60% |
| 69 kV | 60% |
| 110 kV | 70% |
| 115 kV | 70% |
| 132 kV | 70% |
| 138 kV | 70% |
| 150 kV | 70% |
| 220 kV | 80% |
| 230 kV | 80% |
| 275 kV | 80% |
| 330 kV | 80% |
| 345 kV | 80% |
| 380 kV | 80% |
| 400 kV | 90% |
| 420 kV | 90% |
| 500 kV | 90% |
| 735 kV | 100% |
| 750 kV | 100% |
| 765 kV | 100% |
| 1000 kV | 110% |
| 1100 kV | 110% |
| 1150 kV | 110% |
This table is not intended to establish or classify electrical voltage standards in OpenStreetMap.
It merely illustrates how existing voltage values could be grouped for rendering purposes.
Benefits
The proposed rendering would:
- provide an immediate visual hierarchy between different transmission voltage classes;
- make dense power networks easier to interpret;
- preserve the existing
power=towersymbol; - avoid the need for additional voltage labels merely to distinguish network hierarchy;
- use only modest differences in icon size;
- work with voltage systems used in different countries;
- keep towers with unknown voltage visible without visually presenting them as EHV or UHV infrastructure;
- preserve the existing rendering of
power=pole; - require no new OpenStreetMap tags;
- require no modification to existing OpenStreetMap data.
Limitations
Voltage is not a reliable predictor of the exact physical dimensions of a transmission tower.
Tower dimensions and appearance also depend on factors such as:
- number of circuits;
- conductor configuration;
- conductor bundle configuration;
- phase arrangement;
- span length;
- terrain;
- suspension or tension function;
- line angle;
- electrical clearances;
- environmental loading requirements;
- tower family;
- national or regional design standards;
- circuits of multiple voltages sharing the same tower.
For example, a large-angle 220 kV tower may physically exceed the dimensions of some 500 kV suspension towers.
Similarly, two towers carrying lines of the same nominal voltage may have very different dimensions.
The proposed scaling should therefore be interpreted only as cartographic differentiation, not as a literal representation of physical tower dimensions.
Alternatives
Keep the existing uniform icon size
OpenInfraMap could continue rendering every power=tower using the same icon size.
This is simple but provides no visual distinction between substantially different voltage classes.
For example, a tower carrying a 35 kV line could have approximately the same visual prominence as a tower carrying a 750 kV or 1000 kV line.
Continuous scaling
Another possibility would be to calculate icon size continuously from the numerical voltage.
For example, icon size could increase mathematically as voltage increases.
However, this would create many small differences in symbol size with little cartographic benefit.
There is no strong reason for a 275 kV tower to appear a few percent smaller than a 330 kV tower, or for a 735 kV tower to differ slightly from a 750 kV tower.
The proposed discrete voltage classes are therefore intended as a compromise between uniform rendering and continuous scaling.
Tagging
No tagging changes are proposed.
Existing OpenStreetMap tagging remains unchanged, including:
Mappers should continue recording observable infrastructure according to existing OpenStreetMap tagging practices.
This proposal should not be used as a reason to add or change tags solely to influence rendering.
Comments
Please use the discussion page for discussion.
Feedback would be particularly useful regarding:
- whether the proposed voltage ranges provide sensible grouping across different national power systems;
- whether 60% is an appropriate fallback for towers whose voltage cannot be determined;
- whether the highest voltage is the best rendering rule for towers carrying circuits at multiple voltage levels;
- whether the 400–599 kV class should use 90%;
- whether the 600–899 kV class is an appropriate 100% reference;
- whether 110% produces excessive visual prominence for UHV networks;
- whether voltage should primarily be derived from connected
power=lineways.
Voting
This proposal is currently a draft. Voting has not started.
When the proposal reaches the voting stage, use:
{{vote|yes}} or {{vote|no}} and sign with -- ~~~~