GIS Lecture 2C Notes PDF

Introduction: The Need for Accurate Spatial Data 1.​ Importance of Data: ○​ Accurate and comprehensive spatial data is essential for creating reliable maps. ○​ Lack of appropriate data can lead to frustration and ineffective mapping. 2.​ Advances in Data Accessibility:...

Introduction: The Need for Accurate Spatial Data 1.​ Importance of Data: ○​ Accurate and comprehensive spatial data is essential for creating reliable maps. ○​ Lack of appropriate data can lead to frustration and ineffective mapping. 2.​ Advances in Data Accessibility: ○​ In the past, GIS practitioners relied on hard-copy maps from libraries or government agencies. ○​ These maps had to be digitized manually for GIS use. ○​ Today, advancements in GIS and internet technologies provide access to large, ready-to-use datasets from online sources. 3.​ Key Takeaway: ○​ Always check if a dataset exists from a reputable source before creating your own. ○​ This saves time and ensures quality, as updates and accuracy are managed by the source agency. Sources of Spatial Data: Spatial data can be obtained from state, local, and federal agencies and is often made available through GIS clearinghouses. State and Local GIS Data Clearinghouses ​ State governments, local governments, and non-profits often maintain GIS data repositories. ​ Examples in Oklahoma: ○​ Oklahoma Water Resources Board: Groundwater and surface water data. ○​ Oklahoma Geographic Information Council: Digital ortho-photography. ○​ Association of Central Oklahoma Governments (ACOG): Local transportation data. ○​ City of Norman: Planning, zoning, and oil/gas data. Federal GIS Data Clearinghouses ​ Federal agencies manage datasets critical for infrastructure, environmental protection, and national security. ​ Examples of agencies and their datasets: ○​ National Geospatial Intelligence Agency (NGA): Global place names database. ○​ US Fish and Wildlife Service: Species distribution and critical habitat data. ○​ US Environmental Protection Agency (EPA): Environmental data.  ○​ National Weather Service: Climate and weather data. Key Federal Data Sources: 1. US Geological Survey (USGS) ​ Produces vector and raster data for natural feature mapping. ​ Common datasets: ○​ Digital Elevation Models (DEMs): Raster data representing elevation. ○​ Digital Ortho Photo Quads (DOQs): Spatially corrected aerial imagery. ○​ National Hydrography Dataset (NHD): Rivers and streams as vector line datasets. 2. US Census Bureau (TIGER Data) ​ Manages topographic and demographic GIS data through TIGER (Topologically Integrated Geographic Encoding and Referencing) products. ​ TIGER includes: ○​ Census geographies: Block groups, census tracts, counties, metropolitan areas, states (vector polygons). ○​ Roadways, railways, hydrography (vector lines). ​ FIPS Codes: ○​ Unique identifiers for census geographies. ○​ Hierarchically structured to reflect geographic nesting. ○​ Examples: ​ State-level: Two digits. ​ County-level: Five digits. ​ Census tract-level: Eleven digits. Significance of FIPS Codes: ​ Facilitate linking tabular data (e.g., population statistics) with spatial data. ​ Example: ○​ A FIPS code (e.g., 40027201201) indicates location in state 40, county 027, and census tract 201201. Importance of Data Familiarity: 1.​ Understanding Dataset Design and Limitations: ○​ Familiarity with datasets (e.g., TIGER or USGS products) is crucial to avoid errors.  ○​ GIS software does not review or validate the quality of maps you produce. 2.​ Common Mistakes to Avoid: ○​ Assuming data capabilities without verification. ○​ Misinterpreting attributes or spatial relationships. ○​ Failing to check for dataset updates or quality issues. 3.​ Responsibility for Accuracy: ○​ As a map creator, you are accountable for ensuring that your maps are accurate. ○​ Inaccurate maps can misinform and may have real-world consequences. Key Takeaways: 1.​ Leverage Reputable Data Sources: ○​ Avoid recreating existing datasets—use state and federal agencies' resources. 2.​ Understand Your Data: ○​ Know the limitations and intended uses of datasets. 3.​ Accountability: ○​ Ensure your maps are accurate and represent data truthfully, as they are often consumed as factual by the public. By following these guidelines, GIS practitioners can save time, improve the quality of their maps, and maintain credibility in their work.