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Hi, I am currently trying to create a time series map showing NDVI across a catchment... I have a bunch of rasters showing NDVI values across the same area, monthly for approximately 3.5 years. I would like to display all these rasters on a single map to show changes in NDVI, however the problem i'm having is that the values that the colours are representing change, due to differences in the max and min values for each raster. This means that it technically wouldn't be accurate to use one single legend for the map; and it would obviously be silly to have 30 - 40 different legends. Is there a way to somehow link the values in the rasters, so the colour ramp and legend represents the same ranges of values for all the rasters? I hope this makes sense! Anna
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09-23-2011
09:36 PM
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Thank you for your help Timothy, it is good to know that I am on the right track. To determine Upslope contributing area I have created a flow direction raster to use in the watershed tool. I tried creating a watershed raster, however I don't think I'm using the correct input for the Pour Point Data. The Arc manual I am using said pour points were the areas I wish to determine the contributing area for, so I input the shapefile of my sample points. Was this the correct step to take? I am unsure which four point field I should be using, as well. When I followed these steps, Arc calculated tiny watersheds for each point (only a few cells) and I'm not sure this is very accurate. You mentioned I should create the watershed raster and THEN extract values for my points. Should I be using something different for my pour points? I hope this makes sense! Anna
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05-10-2011
04:06 PM
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Hi, I am fairly new to using ArcGIS (GIS software in general, actually!) and I am trying to generate info for some points (sample locations) using a DEM. I've tried to figure out how to do this using the manual but am a bit overwhelmed & unsure about the correct methods! Using the DEM, I hope to determine the slope, upslope contributing area and topographic wetness index for each of my sample locations. At present, my sample points are a separate layer to my DEM. Do I need to merge or overlay these points to the DEM before I can calculate slope, UCA and TWI? If so, how is this done? I have not delineated the boundary of the catchment I am working in, and my DEM extends beyond the catchment boundary. I have the catchment boundary in a separate layer - is it possible to clip the DEM using this boundary layer? Is Spatial Analyst the correct extension to carry out these processes? I know this is a lot of questions, but if anyone can help me with just one of them, that would be great! Thanks for your help, Anna
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05-08-2011
04:55 PM
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