Tex. Tax Code § 25.18

(a) Each appraisal office shall implement the plan for periodic reappraisal of property approved by the board of directors under Section 6.05(i). The plan may not include a standard or timeline that prevents the chief appraiser from appraising property as necessary to comply with the requirements of Section 23.01(a).

(b) The plan shall provide for the following reappraisal activities for all real and personal property in the district at least once every three years:

(1) identifying properties to be appraised through physical inspection or by other reliable means of identification, including deeds or other legal documentation, aerial photographs, land-based photographs, surveys, maps, and property sketches;

(2) identifying and updating relevant characteristics of each property in the appraisal records;

(3) defining market areas in the district;

(4) identifying property characteristics that affect property value in each market area, including:

(A) the location and market area of property;

(B) physical attributes of property, such as size, age, and condition;

(C) legal and economic attributes; and

(D) easements, covenants, leases, reservations, contracts, declarations, special assessments, ordinances, or legal restrictions;

(5) developing an appraisal model that reflects the relationship among the property characteristics affecting value in each market area and determines the contribution of individual property characteristics;

(6) applying the conclusions reflected in the model to the characteristics of the properties being appraised; and

(7) reviewing the appraisal results to determine value.

(c) A taxing unit by resolution adopted by its governing body may require the appraisal office to appraise all property within the unit or to identify and appraise newly annexed territory and new improvements in the unit as of a date specified in the resolution. On or before the deadline requested by the taxing unit, which deadline may not be less than 30 days after the date the resolution is delivered to the appraisal office, the chief appraiser shall complete the appraisal and deliver to the unit an estimate of the total appraised value of property taxable by the unit as of the date specified in such resolution. The unit must pay the appraisal district for the cost of making the appraisal. The chief appraiser shall provide sufficient personnel to make the appraisals required by this subsection on or before the deadline requested by the taxing unit. An appraisal made pursuant to this subsection may not be used by a taxing unit as the basis for the imposition of taxes.