Topology and Geographical Survey Instruments

Vector Data

Vector data in geographic information systems (GIS) are used to represent discrete features with precise spatial attributes (Wang et al., 2021). In flood modeling, these features delineate structures and networks with great accuracy. Stream cross-sections are also treated as vector data, which supports simulating disruptions in water flow caused by man-made structures. Their representation in vector format lets the model see how barriers could influence floodwater distribution.

Raster grids are used to depict continuous data fields. Digital Elevation Models (DEMs) use raster data to map terrain characteristics. DEMs provide a continuous representation of elevation across the landscape, which makes them well-suited for hydrological analysis (Moges et al., 2023). These computations are necessary to understand how water travels over a terrain and where it is likely to pool, thus informing flood risk assessments. Another example of raster application in the study is the Curve Number (CN) grid, which quantifies potential runoff based on variables like land cover, soil type, and slope.

Raster grids are also used to calculate flow direction and flow accumulation. Tools such as ArcHydro help generate these grids, where each cell in the grid represents a calculated value based on its relationship to surrounding cells. The flow direction grid shows where water moves from one cell to another, and the flow accumulation grid quantifies how much water gathers at each point. The final step of flood modeling is to compare a calculated water surface grid with the terrain grid to create flood inundation maps. The model subtracts the elevation values from the water surface levels, to show areas where the water is likely to overflow and marks these as flooded. This analysis is performed on a cell-by-cell basis, which is well-suited to the raster format's grid structure.