Local governments (state, county, municipality) may have additional higher-quality data that is not available from The National Map, and these can included LiDAR-derived DEMs, more detailed contours, or other forms of data. For larger areas, a number of approaches can work, including contours available from The National Map at the 1:1million scale (see the Small-scale Datasets section). The vector topographic data are called Digital Line Graphs (DLGs) while the raster topographic data are called Digital Raster Graphics (DRGs). For smaller areas, try downloading raster data at the 1/3 or 1/9 arc-second, and deriving your own contours. Digital topographic map data exists for the United States in both vector (points, lines and polygons) and raster (image) formats. In this tutorial, we will work through the steps to generate various products from elevation data such as contours, hillshade etc. QGIS has good terrain processing capabilities built-in. Contours at this scale will not be detailed enough for small areas, like a city block, and will have too much detail for representing topography over larger areas. This layer is a georeferenced raster image of the historic paper map entitled: Topographical map of the city and county of New-York and the adjacent country. A new and updated version is available at Working with Terrain Data (QGIS3) Terrain or elevation data is useful for many GIS Analysis and it is often used in maps. The National Map also serves as the data source for modern USGS topographic maps such as US Topos and OnDemand Topos. This is suitable for mapping at somewhere around the size of a neighborhood or town. In addition, The National Map provides continuously-updated, seamless datasets for recreational trails, roads, boundaries, structures, land cover, and imagery. Data for Alaska is at a different resolution.Ĭontours are available at a scale of 1:24000. Other skills you will learn¶ Building pyramids for large raster datasets to speed up zoom and pan operations. Some areas have higher resolution data, at 1/9 arc-second (1 point every 3 meters), including SE Michigan. We will use a raster topographic map and create several vector layers representing features around a park. Raster resolution is 1 arc-second (approximatelly 1 point every 30 meters) and 1/3 arc-second (approximately 1 point every 10 meters) for most areas. 3DEP data from the USGS (which has superceded the National Elevation Dataset (NED)
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