added introductory content and resource links to imageryvector

Author: Max Wesley Gosch

episodes/imageryvector.md

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+## Introduction to Data Collection
 
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+An important decision faced at the start of any geospatial project (from making a basic map to advanced spatial analysis) is whether the project requires original data collected in the field or digitized from maps or can make use of pre-existing data captured by others (e.g., colleagues or online sources). For example, vector data for natural features, political boundaries, transportation networks, etc., already exist somewhere on the web and don’t need to be created from scratch. Many vector datasets are freely available on government or open-source websites, while some specialized datasets are sold as commodities. Open access datasets can vary widely by quality and accuracy depending on the methods used to create them, as well as by how much preprocessing and filtering is required to render them useful. It is therefore important to explore the data carefully to see if they will meet your needs.
 
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+## Acquiring Pre-Existing Vector Datasets from Data Repositories
 
+Below is a list of sources of free vector data from public access sources; other data sources specific to your locality will be available from your local or state government’s webpage. Examine the sources and explore the metadata to see how and when the data sources were created to get a sense of their precision and accuracy. Bookmark sites that seem most useful for your classroom or research applications.
 
+- [Esri Open Data Hub](https://hub.arcgis.com/search)
+- [NYU Spatial repository](https://geo.nyu.edu/)
+- [GeoPortal at Tufts](https://geodata.tufts.edu/)
+- [Big10 Geoportal](https://geo.btaa.org/)
+- [Spatial Data Repository](https://spatialdata.dhsprogram.com/home/)
+- [Open Street Maps Data](https://download.geofabrik.de/)
+- [HydroSHEDS](https://www.hydrosheds.org/)
+- [Natural Earth](https://www.naturalearthdata.com/)
 
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