Downloading GIS data from NJSHAD
- To download GIS data from NJSHAD, first create a query that produces a map. In the upper right-hand corner
of the map view, open the "Layers Control" menu if it is closed.
A blue "Download Layer" button will be visible next to the map layers that are available for download.
- Clicking the 'Download' button opens another browser window displaying a wall of text. This text constitutes
an array of feature definitions and coordinates that make up a GeoJSON file. GeoJSON is an open-source
- To save the GeoJSON text as a file, right-click and choose Save As...
- The resulting .json file can be viewed and manipulated in GIS desktop software. ESRI's ArcMap is a widely
used product, and the free, open-source program QGIS is another popular choice. Slightly different procedures
are necessary to use a GeoJSON file with these programs.
Using a GeoJSON in ESRI ArcMap
- GeoJSON files from NJSHAD cannot be directly opened in ArcMap; they must first be transformed into the ESRI
shapefile format (.shp). Several options are available, but one easy method to transform GeoJSON files into
shapefiles is to use the free, open-source, on-line transformation tool available here:
- Copy and paste the entirety of the .json text into the interface window. Download and unzip the resulting
shapefile to your directory of choice, and load into ArcMap as usual.
Using a GeoJSON in QGIS
- QGIS is a free, open-source GIS program licensed under the GNU General Public License. It runs on Linux,
Unix, Mac OSX, Windows, and Android, and supports numerous vector, raster, and database formats and functionalities.
The program can be downloaded at: http://www.qgis.org/en/site/.
- After installation, two main GIS programs will be available: QGIS Browser and QGIS Desktop. QGIS Browser is a GIS
file explorer (similar to Windows Explorer, but only displaying GIS-related files). QGIS Desktop is the program
where data are displayed, symbolized, and analyzed.
- In QGIS Desktop, the "Manage Layers" toolbar contains an "Add Vector Layer" button. Using that interface,
navigate to the folder containing the .json and open the file. QGIS Desktop can open the .json directly,
with no preliminary transformation being necessary. The .json can then be transformed to a different GIS
file type (including shapefile) by right-clicking the layer name, and using the "Save vector layer as" command.
Important Note About Downloaded NJSHAD GIS Data
- The boundaries of all the GIS layers that are displayed and downloaded from NJSHAD represent slightly generalized
versions of the actual geographic areas. Using simplified polygons reduces overall file sizes, which helps keep
the NJSHAD web-mapping service operating smoothly and responsively. These generalized geographies are perfectly
suited to viewing data distributions at the map scales that are available in the online NJSHAD maps.
- However, downloaded NJSHAD GIS boundaries are generalized, and do vary slightly from official US Census GIS data,
for example (only on the order of several feet, in most cases). Hence, if more precise GIS spatial analysis and
presentation is required, fully detailed GIS files will need to be found from an alternative source.