http://nrm.salrm.uaf.edu/~dverbyla/nrm338 1 Features are points, lines , and polygons Raster themes are grid cells that can represent categories or quantities ArcGIS can display Arc/Info grids, ERDAS imagine rasters, or tif rastershttp://nrm.salrm.uaf.edu/~dverbyla/nrm338 2 Three major raster formats that are understood by Arcmap and ArcCataloghttp://nrm.salrm.uaf.edu/~dverbyla/nrm338 3 You can create rasters using a tool from a text file with keywords such as NCOLS, NROWS, etc.http://nrm.salrm.uaf.edu/~dverbyla/nrm338 4 The ASCII to Raster tool creates a raster. If you do not give the output raster a .img or .tif extension, then the output is an Arc/Info grid.http://nrm.salrm.uaf.edu/~dverbyla/nrm338 5 Longer file names are sometimes nice for descriptive purposeshttp://nrm.salrm.uaf.edu/~dverbyla/nrm338 6 Raster attribute table is not created if raster is floating point.http://nrm.salrm.uaf.edu/~dverbyla/nrm338 7 Raster pyramids are useful for rapid display of large rastershttp://nrm.salrm.uaf.edu/~dverbyla/nrm338 8 .ovr and .rrd are files (reduced resolution dataset)http://nrm.salrm.uaf.edu/~dverbyla/nrm338 9 USGS topo maps are available in Alaska at several scales 1:25,000 is the largest scale, 1:250,000 is the smallest scalehttp://nrm.salrm.uaf.edu/~dverbyla/nrm338 10 You can download scanned USGS topo maps as geotiff files from the AGDC websitehttp://nrm.salrm.uaf.edu/~dverbyla/nrm338 11http://nrm.salrm.uaf.edu/~dverbyla/nrm338 12 Scanning density is the sampling rate in terms of cells sampled per inch of map paper Each pixel is 1/250 or 0.004 inch wide and long covering the maphttp://nrm.salrm.uaf.edu/~dverbyla/nrm338 13 1:250000 map series…each map covers 1 degree of latitude by 3 degrees of longitudehttp://nrm.salrm.uaf.edu/~dverbyla/nrm338 14 When computing distance represented by a map measurement, Make sure your units cancel out…1 cm represents 2.5 km on the map.http://nrm.salrm.uaf.edu/~dverbyla/nrm338 15 How wide is a DRG pixel from a 1:250000 map?http://nrm.salrm.uaf.edu/~dverbyla/nrm338 16 The 1:63360 map series has a naming convention of Columns 1through 6, increasing with increasing western longitude Rows A through D, increasing with increasing northern latitudehttp://nrm.salrm.uaf.edu/~dverbyla/nrm338 17 When computing distance represented by a map measurement, Make sure your units cancel out… 1 map unit represents 1 mile on the groundhttp://nrm.salrm.uaf.edu/~dverbyla/nrm338 18 A pixel is 6.43 meters wide from a 1:63360 DRGhttp://nrm.salrm.uaf.edu/~dverbyla/nrm338 19 Each 1:63,360 map may be mapped at a larger scale (rare in Alaska, common in lower 48)http://nrm.salrm.uaf.edu/~dverbyla/nrm338 20http://nrm.salrm.uaf.edu/~dverbyla/nrm338 21 DRGs are rasters that are scanned from the USGS topo