Mapping Center

In the next couple of blog posts, we want to explain a bit about the two tools you can use to create buffers in ArcGIS. Buffers are used not only in analysis of distances and areas around point, line and area features, they are also used in mapping to achieve a number of cartographic effects, such as coastal vignettes. Since there are two tools and multiple methods you can use to create buffers, and each have their particular strengths and weaknesses, we thought it would be good to review these for you. In the next couple of blog posts, we'll describe the tools and methods, how they differ and what you need to consider when using them. Read More...

This post, is to announce the release of a map template for historical GIS called Historical GIS:  Boston 1775. If you’ve never given historical GIS a second, or a first thought, you might find the contents interesting and maybe even applicable to your work. Consider that the vast majority of GIS data is historical, even if it’s only a few minutes old. Read More...

You will often be prompted to select the geographic transformation when you are projecting data or setting the projection of a data frame in a map document. Here are some concepts that might help you understand what this is all about AND how to make the right selection.

First, "geographic coordinates" are expressed in terms of latitude and longitude. "Latitude" is the north-south angular measure from the equator to the point of interest. "Longitude" is the east-west angular measure along the equator from the prime meridian to the point of interest's longitude. Assuming that the earth is a sphere, geographic coordinates are determined relative to the center of the sphere - these coordinates are called "geocentric latitude and longitude". (See the figure at the right; all figures are from Map Use: Reading and Analysis, 6th edition, ESRI Press.) Read More...

From time to time we've had to create some building footprint data. A colleague was in my office yesterday looking at the map to the right, and remarked that he thought that adding building footprints to maps "humanizes" the map. An interesting observation, and one that I'm not inclined to argue against.

We've learned a few tricks for making haste with little or no waste to produce building footprint data. Read More...

We’ve blogged about symbolizing hillshades (rasters that are derived from elevation raster datasets, like DEMs, via the Hillshade tool), but never really covered the basics of the data used to create hillshades, so we wanted to take a minute and share a few best practices we’ve been adopting.

Before getting started, though, it’s worth noting that we’ve been storing our rasters in file geodatabases. For us, these included some rather large hillshade datasets, ranging between 5Gb and 60Gb. Read More...

We’ve been compiling a list of "What I wish I had known about ModelBuilder before I started using it". Here are a few things that made the list:

1. Create personalized tools in ModelBuilder: Until a few days ago, I thought Read More...

Most of us use digital elevation models (DEMs) which are raster data sets that represent a continuous elevation surface in which each cell represents the elevation at its location. DEM data are typically available in tiles that are sized to balance ease of data sharing with coverage so that those who need several tiles to cover their area of interest are not overburdened with extensive post-download data processing Read More...

We got a good question on Ask a Cartographer this morning.  The gist of the question was how to go about symbolizing street centerlines so they could be drawn using line symbol widths that reflected, at scale, the actual width of the road (as shown in the image to the left). This is a good cartographic solution because varying the line width adds hierarchy to the roads -otherwise it would be hard for you map reader to know which are wider or more heavily used. Read More...

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...

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...

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...