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A Guide to Data Formats and Sources in ArcGIS for Environmental Scientists

This module introduces environmental scientists to various spatial data formats used in ArcGIS, including vector, raster, and coverage types. Learn about points, lines, and polygons in vector data, and discover imagery and land cover in raster formats. Understand the key differences between these formats, including resolution and storage methods. Also, explore valuable data sources, including ESRI data, federal clearinghouses, and regional GIS data portals. This comprehensive guide will enhance your ability to manage and visualize spatial data for environmental research.

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A Guide to Data Formats and Sources in ArcGIS for Environmental Scientists

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  1. Introduction to ArcGIS forEnvironmental ScientistsModule 1 – Data VisualizationChapter 2 – Data Formats and Sources

  2. Chapter 2 Objectives • Basic information about different data formats • Managing spatial data • Where to find spatial data

  3. Vector Data • Points (cities, monitoring stations) • Lines (roads, rivers) • Polygons (political or natural boundaries) • Stored as X,Y coordinates • Each feature has one or more attributes associated with it

  4. Raster Data • Imagery – satellite, digital aerial photos • Land-cover, elevation, and many others • Stored as a rectangular matrix of square cells • Resolution defines the size of the cell • Each cell usually has a single value associated with it • Values can be integer or floating point

  5. Raster shown at 10 and 30 meter resolutions Raster/Vector Comparison Points Lines

  6. Raster/Vector Comparison Polygon converted to 30 meter raster Polygon converted to 10 meter raster

  7. Coverages • Oldest format, uncommon today • Stored in multiple directories • Can hold multiple feature types • Attributes stored in INFO table(s) • Moving, copying or renaming coverages in Windows Explorer will almost certainly corrupt your data • When exported, stored in .e00 file (called an interchange file) • Cannot be edited in ArcGIS Desktop

  8. Shapefiles In ArcCatalog: • Most common format • Consists of multiple files, must have at least three - .shp, .shx, and .dbf • Can only hold a single feature type • Type can be identified by icon • Attributes stored in dBase table • Can be edited in ArcGIS Desktop In Windows Explorer:

  9. Geodatabases • Newest format, becoming more common • Container for feature classes (can be different geometries), rasters, stand-alone tables • Spatial and attribute information stored in the same database • Fewer size limitations • Faster drawing • Can be edited in ArcGIS Desktop

  10. The Default Geodatabase • New in ArcGIS 10 • Each MXD has one • Default location is <user home directory>/ArcGIS/Default.gdb • Can be changed under File>Map Document Properties… or the Getting Started dialog • Is the default output location for tools

  11. Rasters • GRID – ESRI proprietary format • Imagine (.img), GeoTiff (.tif), MrSid (.sid), many other raster formats are also supported in ArcGIS

  12. Other Formats • Stored in text files or database tables • X,Y coordinate data – usually from GPS • Street address data – a process called geocoding (requires suitable streets or parcel data) can convert addresses to points on your map

  13. Use ArcCatalog for: • Moving • Copying • Deleting • Renaming • Browsing • Metadata - creating, viewing, and editing Data Management Do NOT use Windows Explorer for spatial data management!!

  14. ArcCatalog Preview - used for data browsing Data Management

  15. Metadata • Metadata is data about data • For example, spatial extent, contact information, and projection • EPA Metadata Editor (EME): www.epa.gov/geospatial/eme.html

  16. Metadata ArcCatalog Metadata Used to learn about the data

  17. Data Sources • ESRI Data and Maps – DVDs distributed with every software upgrade, also online at the ESRI website • Federal clearinghouses • USGS National Atlas - www.nationalatlas.gov • USGS seamless server - seamless.usgs.gov • USDA/NRCS - datagateway.nrcs.usda.gov • EPA GeoData Gateway - https://geogateway.epa.gov/geoportal/catalog/main/home.page • EPA OTOP Geodata and tools (EPA only) – intranet.epa.gov/rtpgis/geodata.html • EPA Data Finder http://www.epa.gov/datafinder/ • EPA Regional offices

  18. Data Sources • State and local agencies • Most states have GIS data portals/clearinghouses • Many counties have GIS departments • Universities can also be a good source, for example, www.lib.unc.edu/reference/gis/onlinedata.html

  19. Map Services • Geography Network – Hosted by ESRI, built into ArcGIS • igeo.epa.gov – EPA intranet only • Geodata.epa.gov

  20. Some National GIS Datasets • Land-cover – 1992, 2001, 2006 and change, www.mrlc.gov • Elevation – NED, 30 meter resolution, ned.usgs.gov • Hydrology – NHDPlus, www.horizon-systems.com/nhdplus • Soils – STATSGO, datagateway.nrcs.usda.gov • SSURGO is finer resolution, but not available for the entire country • Roads – ESRI Streets data – on the ESRI data and maps DVDs, and TeleAtlas – OTOP website • Demographics – US Census Bureau, www.census.gov

  21. Regional/Local GIS Data • Placeholder to be customized for each location/Region

  22. Imagery • EarthExplorer – USGS site with free download of aerial photography, Landsat and other satellite imagery – edcsns17.cr.usgs.gov/EarthExplorer • GlobeXplorer ImageConnect – link from OTOP page

  23. Water quality GIS data • NHD plus – www.horizon-systems.com/nhdplus • EPA WATERS – www.epa.gov/waters/data • NADP – nadp.sws.uiuc.edu/data • USGS NWIS – water.usgs.gov • WBD – www.ncgc.nrcs.usda.gov/products/datasets/watershed

  24. Air quality GIS data • CASTNet – www.epa.gov/castnet • EPA Air data – www.epa.gov/air/data • AIRQUEST – intranet.epa.gov/oar/airquest (EPA only)

  25. Human health GIS data • Often collected by county, and not always in GIS friendly formats, or even digitally • CDC – www.cdc.gov • Census Bureau – www.census.gov

  26. Creating Your Own Data • There is an extensive set of editing tools in ArcGIS. We will cover them in chapter 8. • You can add point, line and polygon graphics to your maps using the drawing toolbar • You can also convert graphics to features for the ability to add attributes, useful in display and analysis

  27. NHD 1:100,000 NHD 1:24,000 Scale, Extent and Resolution Small scale, lower resolution (less detail) Large scale, high resolution (more detail)

  28. Troubleshooting • A red exclamation point next to a layer indicates the path to the data is broken. To correct the path, right click the layer and choose Data>Repair Data Source from the context menu. • A gray check in a layer’s checkbox means the layer is not visible because the map is not at an a appropriate scale. Zooming in or out (depends on the layer) will make it visible.

  29. Coordinate Systems/Projections • Required to display 3D data in 2D • Projection and datum should be included in metadata • Data acquired from different sources (or even the same source) may be in different projections and/or datums • Good database management practice is to keep all data in the same coordinate system, NOT geographic (lat/lon) • Use the Project tool to convert from one projection to another • If at all possible, avoid projecting rasters • More on projections (and datums) in chapter 5

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