Wash. Rev. Code § 84.40.160
The assessor shall list all real property according to the largest legal subdivision as near as practicable. The assessor shall make out in the plat and description book in numerical order a complete list of all lands or lots subject to taxation, showing the names and owners, if to him or her known and if unknown, so stated; the number of acres and lots or parts of lots included in each description of property and the value per acre or lot: PROVIDED, That the assessor shall give to each tract of land where described by metes and bounds a number, to be designated as Tax No. . . . ., which said number shall be placed on the tax rolls to indicate that certain piece of real property bearing such number, and described by metes and bounds in the plat and description book herein mentioned, and it shall not be necessary to enter a description by metes and bounds on the tax roll of the county, and the assessor's plat and description book shall be kept as a part of the tax collector's records: AND PROVIDED, FURTHER, That the board of county commissioners of any county may by order direct that the property be listed numerically according to lots and blocks or section, township and range, in the smallest platted or government subdivision, and when so listed the value of each block, lot or tract, the value of the improvements thereon and the total value thereof, including improvements thereon, shall be extended after the description of each lot, block or tract, which last extension shall be in the column headed "Total value of each tract, lot or block of land assessed with improvements as returned by the assessor." In carrying the values of said property into the column representing the equalized value thereof, the county assessor shall include and carry over in one item the equalized valuation of all lots in one block, or land in one section, listed consecutively, which belong to any one person, firm, or corporation, and are situated within the same taxing district, and in the assessed value of which the county board of equalization has made no change. Where assessed valuations are changed, the equalized valuation must be extended and shown by item.
The assessor shall prepare and possess a complete set of maps drawn to indicate parcel configuration for lands in the county. The assessor shall continually update the maps to reflect transfers, conveyances, acquisitions, or any other transaction or event that changes the boundaries of any parcel and shall renumber the parcels or prepare new map pages for any portion of the maps to show combinations or divisions of parcels.
RCW 84.40.160