Module 5: How to Generate Contours in ArcGIS for Desktop

this is Logan Hall with the Eastern Shore Regional GIS cooperative and you're watching a video tutorial on how to generate contours in arcgis for desktop appropriate usage for contours can be used for base maps and general typographic visualizations contour should not be used in place of point cloud data or de ends for surface analysis our objectives in this tutorial are comparing raw or smooth contour lines generating contour lines and arcgis for desktop in building a contour index contour lines are used as a familiar medium for representing the elevations of a land surface above sea level these lines are typically used for base maps and general topographic representation contour lines do this appropriately contour should not on the other hand be used for analyzing the surface elevations above and beyond for aesthetic purposes typically when someone mentions contour lines the first thing they think of is a topographic map with smooth rounded curves such as the following example the problem with the sample shown resides at the fact that it inaccurately represents the land surface the point cloud is interpolated to a de M which is then further interpolated into polylines in this particular data set the DTM has been smooth through a process of focal statistics from this resulting raster polylines are generated creating smooth contours if contour lines are generated from the raw DTM you can expect them to look similar to this if smooth contour lines are in fact the desired final product we must do so with a data-driven process this is critical to preserving the data's accuracy in minimizing the level of error we should not generate contours and smooth the vector lines after they have been built this method does not determine the direction and level of smoothing based on the de m or the elevation values themselves this would be an incorrect method of smoothing since it is not data driven and therefore nullifies the accuracy of our already interpolated data the appropriate method for generating smooth data-driven contour lines is by smoothing the input de m using a tool such as focal statistics and ArcGIS or desktop the resulting output will be data driven and will allow us to build contours at different levels of smoothness this leaves control at the user's hand in this tutorial you can assume that you are familiar with accessing the maryland lidar image services as well as extracting from image services in arcgis for desktop for more information on these previous tutorials please refer back to the appropriate documentation we'll start off by bringing in our exported raster data set this is clipped from the Baltimore County de m and meters elevation units and we need to check to make sure our spatial analyst extension has been turned on to customize drop-down to extensions to make sure our extensions are activated particularly spatial analyst since our de M is currently in meters elevation units we need to convert this to feet so using the raster calculator spatial analysts geoprocessing tool will double click our layer variable using the icons within the window use the multiplier 3.2 8:08 for the conversion from meters to feet elevation units select your output workspace folder and name your output raster we can remove our original TEM in meters elevation units in order to create smooth contour lines we first need to smooth our DDM to ensure the vector output is data-driven the most efficient way of doing so in arcgis for desktop by using a focal statistics tool in the spatial analyst toolbox using the search bar select your focal statistics tool are equipped baltimore de m and feet elevation units will be our input raster navigate to your output workspace folder and name your output raster this case name underscore nine since we'll be using a nine by nine neighborhood and a focal statistics ensure neighborhood is rectangle with a height of 9 and a width of nine and then click OK if we turn the layer on and off you may not notice a significant difference between the original TEM and feet and the new D run through focal statistics however this output raster should not be used for any processing other than aesthetic contour building using the search bar will search for contour spatial analyst tool and will generate to contour datasets the first one focal statistics smooth D navigate to your output workspace folder and name your output feature class contour interval of 1 and click OK note that contour lines can be very large depending on your area of interest therefore it is recommended to work within a file geodatabase in ArcGIS countywide contour lines at 1 foot intervals can easily exceed the 2 gigabyte limitation set on shape files so for the second run we'll use our baseline de m and feet without focal smoothing we'll navigate to our output workspace folder then we'll generate a new file geodatabase double click to open your new geo database and name your output feature class contour interval of 1 we'll click OK to run we turn off the baseline DMS zoom into an area we can see the smooth contour lines in comparison to the raw contour lives indexing your contours after they have been generated is an efficient way to set up labels and symbology across multiple intervals first we'll bring in our contour dataset right-click the data set an open attribute table under table options we're going to add a field named index type short integer and click OK right-click our new field open field calculator if you're outside of an edit session click yes we're going to set up a modulo operation for our expression which will be index equals contour space mmod parentheses 10 in computing this modulo will return the remainder of a number after dividing it by another in this particular expression we set a modulo of 10 a value returned of zero will indicate the template interval or index for the contour lines click OK close the attribute table from here we can select our 10 foot index using the Select by attributes or index equals 0 click apply or clear selection navigate right into the layer properties by double clicking or right-clicking access layer properties and we'll set up index labels by first checking label features and the drop-down will define our classes our label is going to be contoured I'm using an SQL query you can select contours or index equals 0 click apply to check our labels and zoom in now we can go back into layer properties under symbology select categories the value field will be index we'll add a single value index equals 0 we have 10-foot contours so click OK double click the symbol we can set this to whatever we'd like in this case we'll do color red with two width and then all other values will be colored black gray width of one click apply and click OK now see we have a one foot contour data set with highlighted 10-foot intervals that are labeled accordingly for additional resources please visit I met Maryland gov and to access your maryland lidar topography server visit lidar GData md gov /i map

Channel: StateMaryland

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Length: 13min 17sec (797 seconds)

Published: Thu Jun 29 2017