The Supreme Court explained the nature of a special assessment in Knox v. City of Orland (1992) 4 Cal.4th 132, a pre-Proposition 218 case. "A special assessment is 'levied against real property particularly and directly benefited by a local improvement in order to pay the cost of that improvement.' " (Knox, at p. 142.) "The essential feature of the special assessment is that the public improvement financed through it confers a special benefit on the property assessed beyond that conferred generally. " (Southern Cal. Rapid Transit Dist. v. Bolen (1992) 1 Cal.4th 654, 661.) A tax is different from a special assessment. Unlike a special assessment, a tax may be levied without regard to whether the property or person subject to the tax receives a particular benefit. (Knox v. City of Orland, supra, 4 Cal.4th at p. 142.) The voters approved Proposition 218, the Right to Vote on Taxes Act, in November 1996. (Apartment Assn. of Los Angeles County, Inc. v. City of Los Angeles (2001) 24 Cal.4th 830, 835.) Proposition 218 can best be understood as the progeny of Proposition 13, the landmark initiative measure adopted in 1978 with the purpose of cutting local property taxes. (Howard Jarvis Taxpayers Assn. v. City of Riverside (1999) 73 Cal.App.4th 679, 681.) One of the principal provisions of Proposition 13 "limited ad valorem property taxes to 1 percent of a property's assessed valuation and limited increases in the assessed valuation to 2 percent per year unless and until the property changed hands. To prevent local governments from subverting its limitations, Proposition 13 also prohibited counties, cities, and special districts from enacting any special tax without a two-thirds vote of the electorate. " (Howard Jarvis Taxpayers Assn. v. City of Riverside, supra, 73 Cal.App.4th at pp. 681-682.) Local governments found a way to get around Proposition 13's limitations, owing in part to a determination that a "special assessment" was not a "special tax" within the meaning of Proposition 13. (See Knox v. City of Orland, supra, 4 Cal.4th at p. 141.) As a consequence, a special assessment could be imposed without the two-thirds vote required by Proposition 13. (Howard Jarvis Taxpayers Assn. v. City of Riverside, supra, 73 Cal.App.4th at p. 682.) The ballot arguments in favor of Proposition 218 declared that politicians had exploited this loophole by calling taxes "assessments" and "fees" that could be enacted without the consent of the voters. (Apartment Assn. of Los Angeles County, Inc. v. City of Los Angeles, supra, 24 Cal.4th at p. 839.) Proponents of Proposition 218 claimed that "special districts had increased assessments by over 2400% over 15 years" and they argued assessments were unfair, with "the poor paying the same assessments as the rich." (Ballot Pamp., Gen. Elec. (Nov. 5, 1996) argument in favor of Prop. 218, p. 76.) The argument in favor of the initiative claimed that under then existing law, ?an elderly widow pays exactly the same on her modest home as a tycoon with a mansion." (Ibid.) To address these concerns, the electorate approved Proposition 218, adding articles XIII C and XIII D to the California Constitution. (Howard Jarvis Taxpayers Assn. v. City of Riverside, supra, 73 Cal.App.4th at p. 682.) "Proposition 218 allows only four types of local property taxes: (1) an ad valorem property tax; (2) a special tax; (3) an assessment; and (4) a fee or charge. It buttresses Proposition 13's limitations on ad valorem property taxes and special taxes by placing analogous restrictions on assessments, fees, and charges." (Ibid.) Article XIII D imposes both procedural and substantive limitations on a public agency's ability to impose assessments. A public agency must comply with certain notice and hearing requirements before it may adopt a special assessment. (Art. XIII D, 4, subds. (c), (d), (e).) Also, an assessment may only be imposed if it is supported by an engineer's report and receives a vote of at least half of the owners of affected parcels, weighted "according to the proportional financial obligation of the affected property." (Art. XIII D, 4, subds. (b), (e).) A valid assessment under Proposition 218 must also satisfy the substantive requirements of section 4, subdivision (a) of article XIII D. In particular, article XIII D "tightens the definition of the two key findings necessary to support an assessment: special benefit and proportionality." (Silicon Valley Taxpayers' Assn., Inc. v. Santa Clara County Open Space Authority (2008) 44 Cal.4th 431, 443 79 Cal. Rptr. 3d 312, 187 P.3d 37 (Silicon Valley).) "An assessment can be imposed only for a 'special benefit' conferred on a particular property. (Art. XIII D, 2, subd. (b), 4, subd. (a).) A special benefit is 'a particular and distinct benefit over and above general benefits conferred on real property located in the district or to the public at large.' (Art. XIII D, 2, subd. (i).) ... Further, an assessment on any given parcel must be in proportion to the special benefit conferred on that parcel: 'No assessment shall be imposed on any parcel which exceeds the reasonable cost of the proportional special benefit conferred on that parcel.' (Art. XIII D, 4, subd. (a).)" (Silicon Valley, supra, 44 Cal.4th at p. 443.)