§ 160. Department of assessment and taxation; powers and duties of assessors. The assessors shall be the head of the department of assessment and taxation. They shall appoint, to hold office during their pleasure, such deputies, clerks, assistants and subordinates as the board of estimate and apportionment shall prescribe. The assessors and their deputies shall possess all the powers conferred, be subject to all the obligations imposed and perform all the duties appertaining to the office of assessors in the towns of the state in reference to the assessment of property within the city, except as otherwise provided by law. They shall perform all the duties now provided by law in reference to the assessment of property for the purpose of levying taxes and assessments for local improvements, imposed according to law. It shall also be their duty to install scientific systems of assessment with tax maps, unit rules and such other systems and records as may be necessary and to gather and file useful and available information that appertains to the value of property subject to their assessment.