1. A computer-implemented method for computing travel costs across a region having an embedded network, the method comprising steps, performed by a computer, of: obtaining data associated with the network, the network comprising nodes and edges connecting the nodes, wherein the data associated with the edges indicates (i) allowed directions of travel along the edges, (ii) total travel costs to traverse the edges, and (iii) whether the edges are accessible; obtaining a grid representing the region, the grid comprising a plurality of cells covering the region and representing unit costs of travel across the cells; preparing a cost-grid dataset comprising costs for off-network travel between an initial location in the region and the plurality of cells in the grid; preparing, using the computer, a hybrid grid-network dataset comprising network travel costs between nodes of the network, the off-network travel costs between cells of the grid, and travel costs between the network and the grid, wherein the preparing step comprises: rasterizing accessible edges of the network to locate grid cells connecting the network with the grid; identifying, based on the rasterized edges, one or more of the plurality of cells of the grid that are accessible to the network; and computing the network travel costs associated with travel between the nodes of the network, and the travel costs between the nodes of the network and connected grid cells; calculating back-links between elements of the hybrid grid-network dataset, the back-links reflecting travel routes originating at the initial location; storing, using a storage device, the prepared hybrid grid-network dataset and the calculated back-links; and querying the hybrid grid-network dataset and the calculated back-links to identify a route with a minimum travel cost from the initial location to a query point within the region.