Storage device, navigation device, and map database creation method

A map database creation method comprising:

• storing measurement position coordinates of at least two specified sub-blocks, the measurement position coordinates being provided by an external server and being obtained by a measurement, the two specified sub-blocks being included in an island-shaped area on an electronic map and the island-shaped area further including a plurality of non-specified sub-blocks positioned along a road, the non-specified sub-blocks being sandwiched by the two specified sub-blocks that are positioned on respective ends of the island-shaped area along the road;
• calculating an estimation position coordinate of each of the non-specified sub-blocks by a proportion calculation based on the measurement position coordinates of the two specified sub-blocks;
• when a distance between an estimation position coordinate of an object sub-block and a measurement position coordinate of the object sub-block is equal to or longer than a predetermined distance, storing the measurement position coordinate of the object sub-block as the position coordinate of the object sub-block, the object sub-block being one of the non-specified sub-blocks, the estimation position coordinate of the object sub-block being calculated by the proportion calculation and the measurement position coordinate of the object sub-block being obtained from the external server;
• and
• when the distance between the estimation position coordinate of the object sub-block and the measurement position coordinate of the object sub-block is shorter than the predetermined distance, skipping the storing of the measurement position coordinate of the object sub-block.