Where a tract of land is being subdivided, including lands proposed to be used for parks or schools under the duly adopted official plan of the city, the subdivider shall indicate the location of such areas on the subdivision plat. Park sites are to be purchased within two years of the recording date of the subdivision by the city at the appraised raw land value prior to subdivision plus one-half of the cost of grading and paving including curbs, of the portion of any streets that are contiguous to the site. School sites are to reserved for two years, giving the Ida Grove community school district, or successor, the right to purchase the land at the appraised raw land value prior to subdivision plus one-half the cost of grading and paving, including curbs, of any streets contiguous to the site. Should the park or school sites not be purchased within the two-year time limit specified above, the subdivider may then sell them for an alternate purpose as shown on the approved subdivision plat. [Code 1975 § 6-6.0207.]