Mapping Center

I've spent the last few months immersing myself in ArcGIS 9.3, particularly ArcGIS Server and ArcGlobe in order to create some map and globe services and see how they work in ArcGIS clients, Google Earth, and Virtual Earth. These services need to look good and draw fast. One factor that can dramatically influence drawing performance is whether projection-on-the-fly is being used.  Projection-on-the-fly will slow your map down, anywhere from 30% to 1000% slower (depending on the coordinate systems involved). Read More...

Last month I was lucky enough to be invited to the USGS's Digital Mapping Techniques (DMT) conference. Unless you do geologic mapping this conference is likely not on your radar, but suffice to say it worth the effort to get to Moscow, Idaho on many counts.  One is that I met Andrew Wunderlich, who gave a great and detailed presentation on how he has been migrating a base of Adobe Illustrator files to ArcGIS. Read More...

I have recently "invented" a method for simplifying polygon map layers, which seems to give reasonable results. Probably many others have invented it before me, but I would like to present it in order to receive comments and advice on setting the appropriate parameters.

My task was to produce a national soil map suitable at 1:1,000,000 scale on the basis of a 1:200,000 map. The best method would probably be to have a geologist or soil scientist make a complete re-production for the new scale - but we needed a less expensive method. The challenge was to find a technique that would not totally erase soil types represented as many small polygons covering more than half of the area in some regions. Read More...

Making maps with data that were never intended for mapping has it's challenges. One of them is trying to use the names from GNIS (Geographic Names Information System) (U.S. Board on Geographic Names).  Even when someone has gone to the effort of assigning these names to GIS features, the way the names are formatted can create problems.  In the case of the GNIS, the names were formatted for an old-style (i.e., pre-modern search engine) alphabetical index that you could visually scan like a gazetteer in an atlas.  The result is that there are entries like "Great Salt Lake, The" or "Grande, Rio" which need reformatting in order to look correct on a map. Read More...

Have you ever wondered where a feature class came from as you've browsed over one of your geodatabases in ArcCatalog? I think most of us have, and probably more often than we'd like to admit. In the example shown here to the left, I made these datasets a few weeks ago, and I have no idea what "GN" means, and if or how I selected, simplified, or dissolved the data.

There are a couple of things we can do to avoid that puzzled feeling: standardize your feature class naming convention; standardize your geoprocessing.  With the naming convention, I started doing the right thing here, but failed to follow through and leave myself the necessary clues. The data in the image above was also the result of a complex workflow, so rather than start with that, let's cover the basics. Read More...

If you're making a map that is either a large format print map or a map that will be served via ArcGIS Server, squeezing every bit of wasted time out of drawing performance is critical. Don't get tired of sitting there drinking extra cups of coffee watching the word "Drawing", all your layer names, and that little blue globe. If you're finding it stressful to explain when updates will be coming, or the timing for caching the map you are serving, or your map services generate complaints about poor performance, then try the two tips in this entry. Read More...

I've often had the situation where I wanted to use a raster data source as a single-color map background layer, but the cell size or other data processing output resulted in a 'blocky' or 'pixelated' appearance to the data at the map scale I need.  A simple raster-to-vector data conversion served only to recreate the boxes or 'saw-tooth' or 'stair-step' lines from the original raster. The ArcScan extension has tools that reduce or remove this problem, and create an output vector data layer with smooth polygon boundaries or more naturally sinuous lines. Read More...

Which are the 30 or 500 most important of Minnesota’s famous 10,000 lakes?  Next, think about that question from the point of view of making a zoom-able map of the U.S. and how many lakes need to be shown as you zoom in.  That question boils down to how to decide which polygons to show.  Not all polygons are created equally, some are roughly round, some are banana shaped (like ox-bow lakes) some have lots of prongs (like a reservoir formed by U.S. Army Corps of Engineers dam), some are long and twisty like a pretzel. Read More...

In the United States, the Public Land Survey System (PLSS) is a way of subdividing land. The USGS topographic map symbols for displaying PLSS data are an excellent way to symbolize PLSS data on not only topographic maps, but because the topographic symbols are  so well recognized, the same symbols can be used on many other kinds of maps. In the image to the left, the "plus" marker symbol shows where a found corner is located, however, if no corner has been found, then no marker should be shown, leaving a gap that signifies the doubtful location of the corner. Next we will describe how to use cartographic representations to symbolize township, range, or section lines to leave a gap at the corners, allowing corners to be added (as point features) or gaps to be shown. Read More...

Indicating that a street is one-way and which way is valid to travel was a lot harder than it should have been prior to version 9.2.  At 9.2, the new representations symbology makes this a much faster and easier task.  To create this effect, you will need to have your street line data stored in a geodatabase which is a requirement for using representation symbology.

You will also need to have a field in your data that indicates whether a street is one-way. This also depends on the digitized direction of the street lines to align the arrows in the correct direction. If your streets are not digitized correctly, you can edit them by selecting each feature, set the Edit task to Modify Feature, then right click on the feature and choose Flip. Read More...

When an elevation raster dataset contains values for both topography and bathymetry, often the best solution to this is to split it into two new rasters:  one for the topography and one for the bathymetry. The reason is that symbolizing this data is difficult. This is because a color ramp that contains appropriate hues for both bathymetry and topography must be adjusted so that it shows the shoreline exactly in the right place, at zero elevation. Read More...