Tag Archives: Blog
by Lara Saikali, Cartographic Product Engineer, Esri. Several community resource centers are available through the ArcGIS Resource Center, including a page dedicated specifically to Hydrology. The Hydrology Resource Center is an online community center that promotes hydro information products created … Continue reading
By Aileen Buckley, Mapping Center Lead, and Simon Woo, Raster Product Engineer
With the update to the ArcGIS blogs as a result of creating a single blog that reflects ArcGIS as a system, you can now find more easily useful map-related information in posts from some of the other teams.
In this blog entry, we point out a number of posts that have been published on the Imagery blog that may be of interest to the Mapping Community. And conversely I note a number of Mapping blog posts that may be useful to the Imagery community. These blog posts will now appear if you search in either the Imagery or the Mapping category.
As you may have noticed, the blog format has changed. The previous system, with a separate blog for each development team, resulted in 100 different blogs that you might follow. The new system is a single ArcGIS blog, where each topic is flagged by category (in addition to its search tags).
One of the Industry Communities categories is Defense, so you can easily find all the Defense-themed blog posts. To just see Defense blog posts, scroll down the main blog to the Industry Communities category list (on the left panel) and click Defense.
The new system allows blog posts to be tagged with multiple categories, so if we see another team’s post that bears on Defense, we can bring it to your attention by adding it to the Defense category. We encourage you to check out the posts in other categories. The Imagery category, for example, contains some content that may be of interest to the Defense community.
You can also add the Defense category feed to your RSS reader:
or bookmark the Defense category:
By Aileen Buckley, Mapping Center Lead
You may have noticed some changes in the Mapping Center blog. As noted in an earlier blog entry, we are updating the entire Mapping Center web site. An exciting part of the update to our blog is that you can now find—in one location—other entries that are useful and interesting to you. The ArcGIS Blog contains entries for area that are very related to mapping, such as 3D GIS, Analysis & Geoprocessing, Geodata, and Services. Continue reading
The new Geonames Tools toolbox is available for download from Arcgis.com. The Geonames Tools toolbox is an Esri Defense toolbox for intelligence analysis. The zip file contains the tools and a template geodatabase with the schema needed to create a gazetteer style locator from National Geospatial-Intelligence Agency (NGA) UTF-8 encoded tab-delimited geonames text files.
The package includes two tools, with supporting scripts, and instructions for using the tools to create your geonames gazetteer locator. The first tool loads data from a UTF-8 encoded, tab-delimited geonames text files into a feature class, updating the Admin, Country, and Feature codes in the process. The second tool creates a gazetteer style locator from the feature class. This locator can be used on a local machine, or published via ArcGIS for Server for use by multiple clients.
This toolbox is designed to work with the files from NGA, available at:
Geoname files from other sources with different formats are not supported.
Geoprocessing can be used to automate many aspects of data compilation, including implementing a geodatabase topology. In my previous post, I created a model that imports data into a file geodatabase and performs initial data cleanup processing. Now, I will use geoprocessing with Python scripting to build a topology on the imported data. Although many spatial integrity issues were resolved by running the model, a geodatabase topology can help check for and repair any remaining errors.
The dataset I am using is a feature class of parcel lot line boundaries that began as a CAD file full of topological inconsistencies, such as lines that overlapped or did not connect to other lines. Once I create the topology and am sure the lines are correct, I will build parcel polygons from the lines and introduce all the features into my production enterprise geodatabase.
Creating a topology in a script
To build topology in an automated manner, I am going to write a simple Python script, add it to a toolbox, and run it as a regular geoprocessing tool. Essentially, the script just performs the functions of the New Topology wizard, but without requiring my intervention. In fact, this script could be developed without any programming by creating a model to perform these tasks and exporting it from ModelBuilder as a Python script.
When scripting, the ArcPy site package allows Python to access and run any of the geoprocessing tools in the ArcGIS system toolboxes, including the topology tools. The Topology toolset in the Data Management toolbox contains all the tools I need to add a geodatabase topology to the line feature class. The import arcpy statement adds ArcPy to a script and is at the top of every ArcGIS Python script.
Before I start adding the tools to the script, I define variables for the paths to the feature dataset, feature class, and topology. Because I created folders to store my tools and data following the recommendations in A structure for sharing tools, I can make the script more portable by setting these paths in relation to the folder containing the script. Since the folder locations are not hard-coded to match the C: absolute path of my hard drive, the script should run on someone else’s machine regardless of the machine’s directory structure.
With the paths defined, I first use the Create Topology tool to add a topology to the feature dataset. The syntax for the tool in my script is arcpy.CreateTopology_management(featureDataset, topologyName, “”), where CreateTopology is the name of the Create Topology tool, _management is the toolbox in which it resides, featureDataset is a variable I defined earlier representing the path to the feature dataset, and topologyName is a variable for the name of the topology. When working with topology, it is recommended to use the default cluster tolerance, which is the distance in which vertices are determined to be coincident. Since I want ArcGIS to calculate the cluster tolerance, I left the value blank as “”instead of supplying one.
Although that function creates a topology, it is currently empty and has no classes or rules in it. I can use the Add Feature Class To Topology tool to add my line feature class with the statement: arcpy.AddFeatureClassToTopology_management(topology, featureClass, “1″, “1″). If the topology contained multiple feature classes, I can set ranks so the feature class with the highest accuracy is not adjusted to match vertices in a feature class which is known to be less accurate. However, since I am using only one feature class, I leave the rank parameters as “1″.
Next, I set which topology rules to include by calling the Add Rule To Topology tool. When choosing which rules to add to a topology, there are a few rules that many editors commonly add to every topology, such as the line rule for Must Not Have Dangles. In the script, this rule is coded as arcpy.AddRuleToTopology_management(topology, “Must Not Have Dangles (Line)”, featureClass, “”, “”, “”). Because the rule only applies to one feature class that does not have subtypes and is not a rule between two feature classes or subtypes, the other parameters are left blank. I also want to make sure that the lines do not overlap or intersect themselves, so I include the Must Not Overlap and Must Not Self-Intersect rules as well. If I need to add more rules later, I can run the Add Rule to Topology tool or use the topology’s Properties dialog box in the Catalog window.
Once all the feature classes and rules have been added, my script validates the topology. The Validate Topology tool identifies features that share geometry, inserts common vertices into features that share geometry, then performs integrity checks to identify any violations of the rules that I defined for the topology. Since the topology has never been validated before, I am going to validate the entire extent of the data with the syntax, arcpy.ValidateTopology_management(topology, “Full_Extent”). However, when working in ArcMap, validating the visible extent of the map instead of the full extent limits the area to be validated and can be useful for very large datasets that take a long time to validate.
Finding and fixing topology errors
After the script runs, I add to ArcMap the resulting topology so I can inspect the results and fix any errors using the ArcMap editing tools. However, with all the previous automated QA work from my Import and Clean Lines model, the remaining manual edits are minimal in comparison to what they could have been without running it first.
The errors identified with topology are indicated by the orange-colored squares. Almost all of these are dangle errors that could not be fixed by the original model since they exceeded the tolerance value for the Extend, Trim, or Snap tools. The topology found only two Must Not Overlap errors, which I can fix by deleting one of the overlapping features. There are no violations of the Must Not Self-Intersect rule, indicating that the lines were split properly in the model. Using the editing tools on the Topology toolbar, such as the Error Inspector and Fix Topology Error tool, I can review each error to determine if the built-in topology fixes can be used or if the lines should be edited manually to resolve the topology error.
In some cases, the topology error may need to be marked as an exception, which is a valid violation of a topology rule. One of the most common examples of exceptions to the Must Not Have Dangles rule is a cul-de-sac road, which are dead ends that do not connect to other roads. However, when working with parcel lot lines, there are fewer scenarios that are valid exceptions. I do have some lines at the edges of the dataset that do not connect to other lines. I can either mark these as exceptions or choose to delete the features, depending on whether these features are supposed to connect to existing features in my enterprise database.
If an edit is made to correct a topology error, I have to validate the topology again to make sure the error no longer exists. After I perform a visual inspection and fix all the remaining topology errors, I can create new polygons representing landownership parcels using the geometry of the lines. If I attempted to create polygons from lines that do not connect to each other properly, either no polygons would be created or one large polygon would result where there should actually be two polygons. After creating the new polygons, I add the polygon feature class to the topology and check for any gaps or overlaps and make sure the parcel polygon boundaries are always coincident with the lot lines.
After implementing the topology and making edits in ArcMap, the lines and the polygons created from them meet standards for our spatial data. I can now introduce the features into the production enterprise geodatabase.
While a script tool or model may take time to set up initially, in the long run, it is quicker to automate data compilation tasks through geoprocessing whenever possible. I can run a tool as needed and re-run it later with different parameters and tolerances or apply it to other datasets. Scripts are particularly useful because they can be run at specified times as a scheduled task in Windows. For example, I could combine the tools presented in these blog entries into a Python script that imports a dataset into a geodatabase, processes it, and implements topology. If I set the script to run automatically in the evening after working hours, I am ready to start editing on clean data when I come into the office the next morning.
For more information:
The sample tools and data can be downloaded from the Editing Labs group on ArcGIS.com. An ArcInfo license in required to run the tools.
Content provided by Rhonda (Editing Team)
A couple of nice additions to the ArcGIS for Desktop 10 basemap gallery were made last week:
1. We added an entry for the new Light Gray Canvas basemap which provides a neutral basemap that makes your thematic data really stand out. There are some useful blog posts about this new basemap on the Mapping Center blog
2. We renamed the ‘Physical’ basemap to ‘Physical and Ocean’ and added the Ocean basemap
into this as a layer. When you add the Physical and Ocean basemap into
your map, you can turn the Ocean basemap on in the entry for this
basemap in the Table Of Contents if you want to see rich detail for the
To add these basemaps into ArcGIS for Desktop 10, choose File > Add
Data > Add Basemap in ArcMap or ArcGlobe. To add them into 9.3 or
9.3.1, choose File > Add Data From ArcGIS Online.
Alternatively, here are the layer packages for the Light Gray Canvas basemap and the Physical and Ocean basemap that you can add directly into your map or globe.
To add these basemaps into your map or globe via the Catalog, make a connection to this ArcGIS server: http://services.arcgisonline.com/arcgis/services
and then add the World_Light_Gray_Base and World_Light_Gray_Reference
services from the Canvas folder, or the Ocean_Basemap service.
Here’s a post on the Desktop blog with more information on accessing the new basemap in ArcMap
A new version of ArcGIS Explorer Desktop (build 1750) has just been released. See the ArcGIS Explorer blog for more information.
Check these locations to download the latest version:
ArcGIS Explorer Desktop is a free, downloadable GIS viewer that provides an easy way to explore, visualize, share, and present geographic information. The latest release of ArcGIS Explorer Desktop (build 1750) delivers fixes and improvements to the previous release. See this previous blog post for a list of new features and capabilities introduced with Explorer 1700.