DAT-241: Geospatial Data Analysis

movie

Session Recording: 9-FEB'21

Map Feature Discovery Exercise Review

Spatial data types

KML

ESRI Shapefile(s)

Map projections and Intro to QGIS

Question: What types of distortion of map features occur as projection systems change? What evidence demonstrates these distortions?

1. Open google Earth and create a test set of about 6 polygons of rectancular and triangular shape which span different axes of the earth. So we want some test features that travel across 1/4 or more of the earth's surface, some extended horizontally parallel with the equator (cutting lines of longitude) and some extending vertically cutting many lines of latitude.
2. Once you have your chosen test shapes, export the file as a KML and upload to your group's directory in the cloud drive.
3. All other group members can then download the test file for use in QGIS
4. Each Member: Create a new project in QGIS named ProjectionComparison
5. With your group, choose 6-8 different projection systems for your project using: Project >> Properties >> CRS tab >> Predefined CRS
6. Look for naming patterns in the CRSs listed and choose from a variety of different core types, using the filter tool to shave down to a certain type of projection, i.e. "Cylindrical" or "Conic"
7. Create a recording system--perhaps a Shared word doc in OneDrive--where you can experiment with projecting your features using several Coordinate Reference Systems in QGIUS. We want to caputre with screen shots the outputs of various projections with some simple explanatory text about what you're seeing.

Target completion for next week 23-FEB

Research the key features of the projections you choose to analyze to add depth to your conclusions;

Session Recordings

QGIS Demonstrations

Spring'21 Session Recording

Recordings

QGIS and Map Layouts

Tool demos

• Intersection: vector >> Geoprocessing >> Intersection. This acts like a "cookie cutter". Be sure to create a new file for your layer and not a temporary layer.
• Export selected features only: use edit >> select and click on features you want to export (click with ctl for multi-select). Then, right click your layer in the layer pane, export >> Save Selected Features As...
• Use Vector >> geoprocessing >> clip to trim points inside a polygon layer
• Dissolve polygons to get an "outline" shape: Vector >> geoprocessing >> dissolve. You can dissolve on a categorical field value if your dataset supports it (i.e. the features are classified based on a category set)

Recordings

Vector Layer Analysis

• Buffers and area overlap analysis

In-Class Exercise Steps

1. Create a blank project called busAccessZones in QGIS
2. Retrieve the Port Authority bus route layer from the WPRDC.org
3. Lets secure contextual layers for identification of regions with poor bus coverage, so perhaps Pittsburgh Neighborhoods
4. With your blank project, click prohject >> properties >> CRS and choose a projected coordinate system, such as the: WGS_1984_Web_Mercator_Auxiliary_Sphere
5. Let's inquire which neighborhoods have the least to access to rapid, express, and key corridor routes. TO do this, let's select only these types of features in our route layer. Open the attribute table. Then click the column header for serviceType to sort by service type. Hold down control and control + shift to select only these three types of routes
6. With only our rapid, express, and key corridors selected, right click the layer in the layer pane, export >> export selected features >> and name the file logically.
7. Create a polygon buffer around all of our Port Authority routes: Vector >> Geoprocessing tools >> Buffer. Once in your tool popup, select the Port Authority routes as your layer, and set buffer distance to 0.25 miles.
8. Consider turning on a base layer with the Quick OSM plugin: Eric used the ESRI World Topo base layer.
9. We now want a new polygon layer of only the neighborhood areas that are not within 1/4 mile of an express, rapid, or key corridor route. Create this with vector >> Geoprocessing tools >> Symmetrical Difference tool.
10. In our case, since the bus routes extend beyond PGH city limits, we need to clip the low-service area symmetical difference layer to only the extent of PGH Neighborhoods. Do this with vector >> geoprocessing tools >> clip
11. Style the result layer and add supporting layers, such as neighborhood centers, etc.

Recording

Applied spatial algorithms

Road Safety mini-projecet

Which sections of road in PA do you classify as most dangerous? Which sections of road are good candidates for increased safety implements such as lighting, guardrails, speed tracker signs?

Suggested steps: Review the PA Crash data points to decide which ones to use in your analysis. Build a map with a reasonable buffer around PA roads such that crashes can be counted with the "Count points in polygon" tool as demonstrated tonight and previously.

Helpful notes

• Eric's PA road buffer is stated in degrees, so his 200 foot buffer was encoded as 0.000549 degrees inside the buffer tool.
• Eric used the weight field in the count points in polygon tool to add additional data depth to the analysis. See tool settings.

Session Recording

Digitizing 311 Service Zones Project

map

QGIS Documentation

map

QGIS Documentation

Session Recording

LandSat 8 Primer and Raster Data

book

LandSat 8 User Guide

travel_explore

USGS Earth Explorer

help_outline

QGIS Raster Data Guide

Project Worktime

Session Recording

311 Project Sharing

Prep postgreSQL install

Session Recording

Final project planning

Recording

Network Data Module

Not to be: Spatial Databases

• PostgreSQL basics
• PostGIS extension installation
• Connecting to PG Admin
• Spatial query visualization

Final project Q&A worktime

Git essentails review