A special assessment may only be levied against parcels of real estate which have been identified as having received a direct and unique "benefit" from the public project.
The special assessment district consists of only those properties which are designated by the applicable law as having received a specific and unique "benefit" from the public improvement.
In the case of a dam ... all properties located within a scientifically defined "watershed" and all properties lying within the floodplain of the dam are connected by how water drains from an entire watershed into a lake and how water within the lake may flood specific areas downstream.
It is also possible that the government unit authorizing a special assessment levy does not have jurisdiction to include all land within the watershed and floodplain.
All classes of properties lying within the distance shoppers can reasonably be expected to walk to and from retail outlets could include a block of homes or an industrial facility.
The commercial properties would be assessed because surveys would illustrate that retail sales depend upon adequate parking for customers.
For example, when water and sewer lines are installed by government units, nearby land often increases in value.
Both the presence of safe drinking water and of sewer lines means that expensive wells and septic systems do not have to be installed by affected property owners.
It also means the potential for contamination of ground water and surface areas from improperly treated sewage will be eliminated.
Providing water and sewer service are situations which may adapt formerly unusable land for residential or commercial use.
This is true in cases where the public's health, safety and welfare are being promoted by the project (e.g. repairs to a dam).
This contrasts significantly with an ad valorem tax which is extracted to fund government operations that are designed to benefit all citizens.
A special assessment is premised upon the necessity for the public improvement and the fiscal burden imposed must be reasonably proportional to the benefit created.
Unlike ad valorem taxes, special assessments are not expected to be uniformly levied (the same millage rate for each parcel).
So, while both properties have identical $5,000 special assessment obligations because sewer installations have been specially assessed, there will be a huge difference in their ad valorem tax levies; one ad valorem levy will be based upon the value of a vacant lot and the other will be based upon the value of the lot plus the million dollar home.
This happens because it is difficult for the ordinary citizen to recognize that an error in the special assessment procedure or methodology has occurred and the resources a taxpayer must use to fight a special assessment levy are more expansive and costly than resources to fight an improper ad valorem tax on their real estate.
Of most importance to any property owner who feels aggrieved by a special assessment levy is a legal concept known as a "presumption of validity".