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Thursday
Jan032013

Street Segments as Units of Analysis: Spatially Joining Points and Lines

Recently, authors David Weisburd, Elizabeth Groff, and Sue-Ming Yang published a book titled The Criminology of Place: Street Segments and Our Understanding of the Crime Problem. The crux of the book is that in Criminology and other disciples have a long history of using geographic units of analysis that are area based. That is, we have become accustomed to using polygons as units of analysis. Part of the reason for the use of area based units of analysis is that demographic and social data are available through sources like the United States Census Bureau. In the book, the authors make a compelling argument that area based studies miss a lot of spatial variation that occurs at lower levels of analysis. In an attempt to combat the loss of information through aggregation the authors show that using street segments as units of analysis may be a viable alternative to area based units of analysis. 

In the spirit of using street segments as units of analysis we thought highlighting how to use Cartographica to aggregate data points to street segments would be a fun and interesting exercise. Recent upgrades to Cartographica 1.4 include the ability to spatially join data based on their spatial association. This includes joining points to lines. 

The data being used in this example are from Washington D.C.'s GIS repository DCGIS. The data are 2011 crime incident locations and a street file containing all of the street segments in the city. To import the data into Cartographica choose File > Import Vector Data. Below is an image of the data described above. At first glance it appears as though the points are "on top of" the line segments. Observe. 

However, upon closer inspection you can see that the points are not directly on top of the lines. As a result, we will need to use a distance based spatial join to join the crime points to the line segments. 

Because we want to join the crime points to the street segments we first need to select the Streets layer in the layer stack. Once selected, choose Tools > Spatial Join. The following image shows the set up for the Spatial Join. Uncheck the Discard Unmatched Features so that the new join layer will have all of the street segments including those that have zero crimes. Note that the "Within Distance" operation is selected and a distance of 50 meters is the designated distance. Also note in the table that the 2011 crime data fields are set to ignore. The reason for this is that at this point we do not need all of the excess crime information. All we want is the counts of crimes on the various street segments. Finally, note that the last field in the table "Join Count" is selected to be copied. This will be the new field on the street segments layer that will contain the crime counts. 

 

After the points are counted and aggregated to the street segments you can reclassify the counts into groups and then vary the street segment colors by the groups. Double-click on the streets join layer in the Layer Stack to brig up the Layer Styles Window. Add three categories to the table by click on the + button. Click on the Gear Box and select Distribute with Natural Breaks (Jenks). Change the colors of each of the categories by clicking on the fill box and choosing a series of colors. See the map below for the final result. 

Friday
Dec282012

Best Open Geodata Release of 2012: Philadelphia Open Data 

With the end of the year approaching everyone is putting out their "Best of" list for 2012. Emily Badger of The Atlantic Cities recently released a list of the "Best Open Data Releases of 2012". These open data sources are available through various agency and government websites and allow users access to data sources that include geospatial data. 

We decided to check out a few of the Open Data sources and wanted to create a few maps using Cartographica. The Philadelphia Open Data website was listed as the best Open Data website of 2012. We were able to download a .csv file for all of the crime incidents in Philly since 2006 from the website. Download the Philly Crime data.  

To start, add a Live Map to use as a baseamp by choosing File > Add Live Map

To geocode the data using Cartographica choose File > Import Table Data. The Import File window will appear. Select the coordinates tab in the top right. Change the Map to selection for the Point X and Point Y fields to X (or longitude) and Y (or latitude) and then click Import. See below for an example of the set up. 

*When we geocoded the Philly Crime data 164 incidents were geocoded to the Cincinnati area. Upon further inspection the points were geocoded to the appropriate location based on the data entries. The X and Y coordinates for all of the 164 incorrect points were, -84.69369121 longitude and 39.1207947 latitude, which places the points at the corner of Salyer Ave and Goodrich Lane just West of Cincinnati. These points were considered erroneous and were discarded. To delete the points select them using the identify tool and then choose Edit > Delete. 

The map below shows the geocoded crime incident points in Philadelphia since 2006. The Philly_Crime layer contains 592,064 crime points. 

You can filter the data by using the Filter bar. Change the Filter bar selection to Text_General_Code and then type in Homicide. The data will be filtered to only show homicide incident locations. Since 2006, there were 3051 homicides in Philadelphia. Use the identify tool to select all of the points and then hold down the option button and choose Tools > Create Kernel Density Map for Selection. The result of the KDM analysis is shown below. The red areas indicate places where homicide was highly concentrated.

 

A closer look at central Philadelphia.

Another way to filter the data is by date. The Philly_Crime layer contains a field called Dispatch_2 that contains the date of the offense. With the Philly Crime layer selected in the layer stack type in 12/31/2010. A small box will appear at the top of the Map Window. You can filter based on multiple criteria to limit the dataset to any year that you want. To select only the 2011 data use the settings shown below. Notice that we are selecting crime incidents that fall between 12/31/2010 and 1/1/2012. 

Use the identify tool to select all of the 2011 crime points and then choose Layer > Create Layer from Selection. The new layer should have 82197 crime points. You can repeat these steps so that you can create a new layer for each of the years in the data set. Create another Kernel Density map by Choosing Tools > Create Kernel Density Map. The result of the KDM analysis for the year 2011 data are shown below. 

Friday
Dec142012

Mapping the Syrian Conflict

The violence associated with the Syrian revolution continues to escalate as recent reports have indicated that Bashar Al-Assad's forces have begun to use SCUD missiles in attempts to drive back rebel forces in the area near the Syrian Capital. SCUD missiles are infamous for their use by former Iraqi dictator Saddam Hussein during the Persian Gulf War. Equally as infamous are the U.S. produced Patriot Missile systems that are designed to eliminate surface-to-surface missile attacks. Recent reports have indicated that American, German, and Dutch patriot missile battalions have been sent to Turkey to eliminate the risk to the Turkish people from possible SCUD missile attacks from across the Syrian border. Check out the article on the Huffington Post about the recent visit from U.S. Defense Secretary Leon Panetta's visit to Turkey regarding the Syrian conflict and the U.S. Patriot Missile response. See below for a diagram from Raytheon for how the Patriot Missile system works. 

In order to add more context to situation we have created a few maps to highlight the areas where the Patriot Missile systems are being deployed. The Patriot Missile systems are being deployed to Kahramanmaras, Turkey, which is about 70 miles North of the Syrian border. We can confirm the distance between Kahramanmaras and Syria by using Cartographica's Live Maps and measurement tools. See the image below for an example. To add a Live Map, Choose Tools > Add Live Map, and to use the measurement tools click on the measure tool button and then drag a line to determine the distance. 

We can also look at the radar and missile ranges of the Patriot Missile systems by using buffers. The radar used by the Patriot Missile system has a detection range of about 180 miles in all directions around the system. The map below shows how far the systems deployed in Kahramanmaras will be able to detect incoming SCUD missiles. To create the map you first need to add a new layer by choosing Layer > Add Layer. Add a new feature to the layer by choosing Edit > Add Feature and then select to add a new Point feature. Create a buffer for the point by Choosing Tools > Create Buffer for Layer's Features. Make the buffer for 180 miles. 

You can add to the map above by also creating a buffer for the effective range of the Patriot Missiles. The range is about 70 miles. Using the same steps as above create a second buffer for 70 miles. The map below shows the results. 

 

Thursday
Dec062012

Using CartoMobile to Enhance Historic Sites

The United States National Park Service maintains and controls more than 84.4 million acres of park land in the United States. Much of the land is historical in nature and has been preserved for future generations to enjoy and learn about the various parks. The use of the parks is as varied as the many historical and ecological characteristics that define each unique location. One of the most popular types of parks within the United States are National Military Parks. These parks are typically located on the sites of famous battlefields and other important historical and strategic locations around the country. Among the popular locations for park visitors is the National Military Park at Gettysburg, Pennsylvania. Gettysburg was the location of one of the most important battles during the U.S. Civil War. The battle lasted three days and there were approximately 53,000 casualties combined. Gettysburg is also the location where Abraham Lincoln gave his most famous speech, The Gettysburg Address. Due to the significance of the battle the Gettysburg National Military Park hosts more than one million visitors per year as they take in the natural beauty of South-Central Pennsylvania and attempt to understand the military and historical significance of the battlefield. 

Having personally been to Gettysburg I can attest to the fact that the battlefield is quite large, and has a wide range of positions that are challenging to understand. This is especially true when you want to know where specific units and specific generals were located on the battlefield. The National Park Service has constructed monuments to give some idea about the locations of various units, but I think we can make the location awareness even better. In the following example, we highlight the ways in which Cartographica's and CartoMobile can be used to improve location awareness in the field. 

The process that is to be described involves a number of steps that we can summarize here.

  1. Locate a map of the positions of both armies. The image can be found by performing a Google search. To streamline the process I decided to only create layers for the infamous Pickett's charge that occurred on the third and final day of the battle. The map I used can be downloaded on the Pickett's Charge Wikipedia page
  2. Georeference the army position map using Cartographica. To georeference the image I used Cartographica's powerful suit of raster tools. To view the process for georeferencing an image check out the following links: Georeferencing Cold War Images, How to georeference images with Cartographica. The process for georeferencing begins by importing a raster image by choosing File > Import Raster Data, and then choosing Edit > Georeference Image
  3. Use the georeferenced image to create a polygon layer. In this step the goal is to use the georeferenced raster image to help draw new polygons in vector format. To draw new polygons first add a new layer by choosing Layer > New Layer. Next choose Edit > Add Feature. You will be prompted to select a layer type, select Polygon. At this point you can begin drawing new polygons by control clicking to add ground control points. The first image below shows the georeferenced Pickett's charge image. 

    The next image shows the new polygon being drawn.

    Note: when you look at the map there are a lot of individual units to draw. To make this process easier you can use Edit > Duplicate to quickly create an identical feature on the same layer. This allows you to quickly duplicate the first polygon you have drawn and simply drag it to the next unit position. For more information on adding features check out the following blog post, streamlining workflow when adding features. 
    The final unit position map (Note: the map below already has attribute data added, which is discussed next).
  4. Enhance the new polygon layers with additional attribute data. In the map above additional attribute data has already been added. Those attributes are the commander, unit size, and casualties of each unit during the battle. This step took a little additional research into what the units at the battle were comprised of. In general, my layers are estimates based on information about unit size, and casualties. Please do not take the numbers here as fact. Much more research is required to be more confident that these numbers are correct. To add a new variable/attribute  choose Layer > Add Column. Next, you can manually enter each unit commander name by typing within the Data Viewer. In my quick research I found that brigades (the army units in the map) were comprised of about 1000 soldiers. Also I found that the Confederates lost approximately 50% of their soldiers during Pickett's charge, based on those number I created the Unit Size and Casualties attributes. 
  5. Export the new polygon layers as shapefiles by choosing File > Export Layer's Features. Save the files to a desired location. 
  6. Use iTunes to add the new army position shapefiles to your iPhone. Open iTunes and sync your iPhone. Go to Apps and click on Cartographica. At the bottom, under File Sharing, click Add and then add the new polygon layers showing the army units. The image below shows what the iTunes set up should look like. (Note, Sallie the Christmas dog at the top!)
  7. Open the new shapefile in CartoMobile for quick reference while visiting the battlefield. See the images below.
         
Friday
Nov162012

Cartographica 1.4 and beyond

At ClueTrust, we're proud and excited to deliver version 1.4 of Cartographica into the hands of our customers.

This has been a long journey from the last major feature release to this one, and although we have added a lot of new functionality to the software and made many improvements, it became clear to us months ago that something was going to have to change for us to be more responsive to the needs of the market and our customers.

To that end, we have been bolstering our automated testing capabilities, enhancing our hands-on testing regime, and changing how we track and execute changes in order to reduce internal dependencies and ensure software quality while shipping enhancements more frequently.

We appreciate the patience that you have shown as we have gone through this transition, and we're excited to be able to move towards a more agile delivery schedule.

As we do so, we encourage all of our customers to use the Feature Requests section of our support site to provide us with ideas for features or enhancements.   We read it regularly and use it to gauge the interest in individual requests.

Going forward, we are setting a goal to release features every 6-8 weeks, and bug fixes between times as necessary.

Thanks again for being patient with us during this transition and we look forward to delivering an even better experience as time goes on.