HomeMy Public PortalAboutExhibit MSD 84H - Impervious Processing RulesImpervious Processing Rules
Geographic Source files:
Parcel boundaries w/ Parcel ID Number (City and county)
Impervious Surface Shapes w/ FC_Name classification (collected by Sanborn from
Aerials)
Rules:
All impervious surfaces are truncated at the property boundary (clipped to Parcel),
eliminating any portion of impervious shape within the ROW
Commercial property is charged for impervious that lies entirely within the
property – impervious shapes are intersected by commercial property boundary.
Residential property is charged for impervious surface whose greatest area resides
on the property. No intersection with parcel boundary is performed. The entire
area for an impervious shape is calculated and assigned to residential parcel
containing the greatest portion.
No roads, private or public, are included in the billable impervious surface
Airports are not charged for “runways”; buildings, access areas, etc are billable.
All chargeable fees are rounded to whole dollar amount
“Driveway” captured in county parks will be re-classified as “road” (non-billable)
per precedent in city parks
“areas under construction” will not be billed
Swimming pools will not be billed – surrounding patio IS billable
Bridges are considered part of pavement and will not be billed
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MSD Amendments to data:
1. Parcels – may be adjusted by mapping staff to correct for data errors, eg: parcel
boundaries that are misaligned to aerial photograph such that majority of structure or
pavement is incorrectly placed in neighbor rather than owner.
Corrected parcel boundaries created visually by mapping staff.
2. Impervious Shapes – may be split manually in residential areas where multi-unit
dwellings straddle dividing property lines. Shared driveways are also split to divide
between multiple owners.
WHY:
Impervious polygons have to be split to calculate appropriate square footage by owner.
Simply intersecting impervious shapes with parcel boundaries fails to equitably split:
Because the parcel does not always cut evenly, due to parcel boundary errors.
RULES:
For all property, impervious area is clipped at the Right-of-Way.
For residential properties, the impervious area is assigned to the parcel with the greatest
portion (eg: driveways or houses that cross parcel lines are charged COMPLETELY to
the one owner)
Exhibit MSD 84H
For non-residential property, the impervious area is bisected by parcel boundaries and the
surface that fall within a non-res property is charged to that property. (eg: edges of
pavement crossing into the neighbor non-res parcel are charged to the neighbor.)
MAPPING EDITS:
Mapping lines = In order to make the data model more accurately represent these
scenarios, the mapping staff has visually inspected the impervious area file and created
“split” lines that can be used to assign impervious square footage to the appropriate
owner. This enables mulit-plex housing to be assigned by “greatest overlap” method.
Adjusted parcels = The mapping staff has also adjusted parcel boundaries according to
the aerial photography, to more accurately represent landowner interests on the ground.
This allows impervious areas to fall upon the majority residential – and to facilitate even
splitting of commercial impervious surface.
Microstation files are converted to shapefile format, then imported as feature classes
into a geodatabase for processing. Area size for efficient processing will be needed.
All files have been converted to NAD83 Stateplane feet, MO East in order to facilitate
this process. Overlay operations do not function properly on layers in varying coordinate
systems.