Hypsometric Symbology With Elevation Rasters

welcome back to GIS analysis at the University of Alaska Fairbanks from last session we downloaded a raster from Alaska and Western Canada which was originally in longitude and latitude and we projected it so now every cell is one kilometer wide and one kilometer high and ultimately we're going to map the Yukon River watershed from this raster the first step we'll do is we'll eliminate any local pits or sinks that might exist in this elevation raster so to do that we can use a geoprocessing called fill so we'll fill our raster if it has a local pit or sink just due to random errors and we'll output it to our home folder and we'll call that filled this really is a minor filling so if we look at we've got the exact same high we have the exact same low the means will be very similar but if there were any local pits they are filled and the way film works if we go to arcgis help learn more about how fill works so basically this is how fill works is here we have elevations and then we have a random error and then it fills that one cell so it matches so now we have we can do things like watersheds without the watershed ending at this local pit that is due to a random error so for the remaining of the session will work with our filled raster so let's remove our original elevation and now we have our filled raster one thing we might want to do is color code our raster so the lower elevations are green and the higher elevations are snow so if we go to properties and under symbology let's pick a color ramp where we have snow at higher elevations and then let's use a 1 standard deviation stretch and then okay so here we have lots of snow at higher elevations so anywhere it's white the elevation is one standard deviation or greater above the mean and if you want it less snow if you go to properties let's do a two standard deviation stretch so now the snow is in areas that are two standard deviations above the mean and if you want even less snow we could do a three standard deviation stretch now the snow is in areas that are three standard deviations above the mean and let's color code our ocean some ocean color to do that if we go to our properties display background values that have zero elevation give it some ocean color and then we can zoom in on okay the other thing we could do with our elevation raster is create a hill shade and we use the hill shade geoprocessing tool to do that we take our elevation raster and then we'll output our raster as our hill shade and and you as a user get to decide where the Sun is in the sky by default it's in the northwest part of the sky for example 90 would mean the Sun is to the east 180 would mean the Sun is to the south 270 would be to the west so 315 is the Northwest and then how high is a sudden at these latitudes the Sun is not above 45 degrees so let's change that to the Sun elevation above the horizon is 25 degrees well create a hill shade with the Sun in the northwest part of the sky as 25 degrees above the horizon there we have our hill shade and we can enhance our contrast by going to properties and then let's give it a standard deviation contrast one standard deviation if you're less than one standard deviation you'll be get back if you're above the mean by one standard deviation or greater you'll be bright white enhances our contrasts now if we take our elevation raster and we change our drawing order so we click on lists by drawing order and drag the elevation raster so it's on top then what we can do is we can change the transparency to see our hell shade below our elevation raster go to properties and display let's try a transparency of 50% now we can see the hill shade below our elevation raster and if you want to fine-tune it if you right mouse click anywhere in the gray and go to effects we can adjust the contrast brightness and transparency let's do a transparency that's less transparent 20% transparent and then let's do a transparency that's more transparent so 80% transparent basically you as a user can dynamically adjust the transparency until you get it the way you want it the other thing we might want is contours of equal elevation create contours we can use the contour tool input raster is always the elevation raster and then we'll output our contours let's say we're gonna have 100 meter contours you would specify what the contour interval is it will have 100 and your contour is starting at sea level notice in the Yukon flats we have very few contours because it's a flat landscape and then the Yukon Quest Co M Delta we have very few contours if we zoom in on the Alaska Range you can see we have lots of contours because it's very rugged topography we're interested in delineating the watershed of the Yukon River and it would be possible to do that by contours you'd have to zoom in so for example here's the Yukon River in this area here what you would have to do is find the ridge line where the watershed drains in the Yukon River versus where it doesn't drain in the Yukon River so it's possible but be very difficult so in the next video session we're going to use an automated method of delineating the watershed based on the flow direction within each pixel

Channel: GIS Analysis NRM435 University of Alaska Fairbanks

Views: 2,141

Rating: 5 out of 5

Keywords: elevation rasters, DEM, arcmap elevation, hillshade

Id: eqbsw39zQk0

Length: 7min 32sec (452 seconds)

Published: Wed Apr 04 2018