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Screenshot from the regulator's zone creation box
Zones with subtraction
Zones with subtraction can also contain all types of policies. However, unlike General zones, they subtract overlapping areas from similar zones below in the zone list. So when a Zone with subtraction overlaps another Zone with subtraction, the overlapping area is subtracted from the underlying zone. This makes it easier to create and edit non-overlapping zones. As an example, you do not have to create the inner part of a "donut zone", it is automatically subtracted from the outer zone.
There is an exemption for fees and subsidies - and for max and minimum limit (vehicle caps). When these policies are applied, the zone must be a Zone with subtraction, to not calculate the accumulated amount twice.
Zones with subtraction also enable so-called stacked analytics, to e.g. monitor vehicle caps of zones, as described in the next section.
Left: Stacked analytics - the three areas sum up to a total. Right: Comparative analytics - the two zones are compared
Analytics
The two zone types differ when it comes to how analytics are displayed. Zones with subtraction can be included in analytics that stack zones on top of each other to show a total for the whole city or municipality.
The General zones on the other hand can not be included in stacked analytics (as that would create issues with double counting). They can however be included in analytics that compare different zones to each other, like comparing different city districts.
Note: New zones will not appear in the analytics page until the day after they were created.
Zones with subtraction A and B punches holes in Zone with subtraction C, thus turning zone B and C into “donut zones”. General zones D and E do not influence the geometry of each other, nor zone C.
Use Example
Typically, a city may have three main zones: An “outer urban zone” (zone C), a “city centre zone” (zone B), and an “inner city zone” (zone A). These zones would be Zones with subtraction, as you want these zones to punch holes in each other (that is, be non-overlapping) in order to count the number of vehicles in all the three zones and generate stacked analytics for monitoring purposes.
In addition to these zones, you would typically have a number of General zones (zones D and E) for policies like slow zones, no-park zones, driving forbidden etc.
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