St Johns River Kilometer Mark

This dataset is a linear referenced St Johns River major channel layer. It is independent of the StJohnsRiver_ReferenceLine layer. Features in this layer have measurement values (relative position from start location), which represent the river mile (from mouth).本数据集为线性参考型圣约翰河（St Johns River）主河道图层，独立于StJohnsRiver_ReferenceLine图层。该图层中的要素包含测量值（相对于起始位置的相对位置），其代表以河口为基准的河道英里数。