Announcements

Task 2

• Opens September 18.
• You can book a visit to the map library now. 🔗

        lat, lon, name
        38.050948,-84.494443,"Gratz Park"
        38.041548,-84.490826,"Thoroughbred Park"
        38.047543,-84.499551,"Big Blue Building Plaza"
        38.046628,-84.496303,"Courthouse Plaza"
          

"a single map is but one of an infinitely large number of maps that might be produced for the same situation or from the same data."

Data

• Observations
• that are interpreted to create information.
• Knowledge exploits information.

Mental map

• A perception of place
• rendered from one's experience and observation.
• Spatially orders imagination.

What if you had

• a different understanding of
• and experience in the world?
• Different knowledge, different map.

Different mappings

• will use different observations
• with different interpretations.
• Maps are arguments.

Your data

• are your observations encoded into a usable format.
• A mental map is one format. It's your argument of how campus is ordered.
• Do we have other ways?

Point locations

• Every thing on Earth has a location and it can be represented as a single point
• using invisible grid of latitude and longitude.

Y axis

• Latitude
• Also called 'parallel'
• Measures distance from equator
• North + or South -
• +36.616323° latitude

X axis

• Longitude
• Also called 'meridian'
• Measures distance from Prime meridian
• East + or West -
• -83.726845° longitude

Greenwich, England

• Prime meridian chosen in 1884
  • because of the invention of clock that could keep time at sea.
  • More about this in the GPS module.

Lat, Lon coordinates

• can locate any place on Earth
• within a foot using ~20 characters
• in decimal degrees number format.
• Example: 36.616323,-83.726845

People hunt

• integer degree intersections.
• What's at 0,0? Null island!
• How about 38,-85? A field near Salt River, KY
• Confluence.org 🔗

A different way

• to locate places on Earth?
• what3words.com divides the world into 3m x 3m squares
• and names the squares with three words.

Criticism

• They claim to save lives.
• What if your house was located with
  • wildcats.fail.today
• It's proprietary:
  • We can't see how they label locations.
  • They charge for conversion to lat, lon.

Models that we'll explore

• Attribute
• Vector
• Raster
• Point cloud

Attribute model

• Table of attributes
  • Row represent an observation.
  • Columns represent attributes for the observation.
  • name, lat, lon , what else can describe what is observed?
• Most common data model.

File formats

• Applications like Excel produce spreadsheets.
• Text-based formats are more portable.
• CSV is the most common text-based format.

CSV file

• Comma-Separated Values
• a delimited text file with a .CSV file extension.
  • delimited: having fixed boundaries.
  • text: readable by humans.
  • file: data stored in a digital document.
• A ubiquitous format for sharing data.

CSV format

• First row of file contain field (column) names.
• Each subsequent row is a data record.
• Each row consists of one or more fields, separated by commas.

🔎 CSV field values

• Two : text and numbers.
• Text values are enclosed in double-quotes ""
  • "Geography, Y'all!"
• Number values are not enclosed in double-quotes
  • -85.7617613

              lat, lon, name
              38.050948,-84.494443,"Gratz Park, Y'all!"
              38.041548,-84.490826,"Thoroughbred Park"
              38.047543,-84.499551,"Big Blue Building Plaza"
              38.046628,-84.496303,"Courthouse Plaza"
                

Vector model

• Encodes location as a coordinate pair (x,y) or (lon,lat)
• in a specific order.
• Includes attribute model.
• Requires mapping software to view.

Geometric primitives

• Point
• Line
• Polygon
• Model what we observe in a simple, yet powerful, way.

Practice making vector data

• Visit geojson.io
• Draw a
• Point
• Line
• Polygon

Example

• of vector data model with
• Pine Mountain State Resort Park
  • Take a tour: First Frontier Audio Driving Tour

Let's build

• the vector layers for Pine Mountain...

General rule for layering

• Polygons on the bottom,
• then lines,
• and finally points on top.

File formats

• Look in this presentation's appendix.

Vector problems?

• Vector best represents discrete features
• those that have obvious edges.
• It's either there or not.

Uncertainty

• How to handle ambiguity
• or subtle variations?

Raster model

• Matrix of cells (pixels)
• Cells are adjacent
• and have a numeric value representing a statistic.
• E.g., average density of forest.

Examples of common rasters

• Land cover & land use 🔗
• Photos showing change on Earth 🔗
• Rasters are good at quantifying subtle variations.

Image raster

• Photographs!
• from airplanes or satellites
• Let's revisit Pine Mountain.

Thematic raster

• Difference of type
• Land cover type

Continuous raster

• Difference of magnitude
• Magnitude of elevation

General rule for layering

• Rasters on the bottom,
• and vary transparency and blending mode to stacked multiple rasters.

File formats

• Look in this presentation's appendix.

Raster fun

• Compare the size of one area to another.
  • Boston Public Library Insizeor project

Point cloud model

• Cloud of points representing x,y,z location.
• Created from laser scans.
• Creates detailed 3D map.

Point cloud fun

• View point clouds online
  • Cesium Ion: UKy Campus
  • Entwine Potree: potree.entwine.io

Local

• Lexington: download
• Louisville: download
• UKy: download
• Kentucky: download

World & National

• Natural Earth: download
• USGS: download

Let's explore data!

• 1. Download data from a source.
• 2. Extract (unzip) the file to your module-01 folder.
• 3. Drag and drop the data into GeoJSON.io.
• 4. Now try QGIS.

Four types of numbers

• Nominal: number is a literal name
  • 1 is a tree, 2 is lake
• Ordinal: number is a rank
  • 1 is preferred over 2
• Interval: quantity with arbitrary scale
  • 0° F is not 0° C
• Ratio: quantity with a true zero
  • 0 is the same in any unit

Maps

• What are they?
• Why can an infinite number of maps be made of the same area?
• Why are maps always wrong – to someone?
• What is a mental map?

Location

• What system have we used to find locations?
• What is the X axis and what does it measure?
• What is the Y axis and what does it measure?
• How many decimal places should we use?

Data

• What is it?
• Explain our four data models.
• What are the data formats used in each model?
• If we see two numbers, how might they be different?

Create workspace

• Create a top-level directory on your computer
• to organize your map projects and data.
• Create a CSV (comma-separated values) file for Lab 1.
• Details in Lab documentation.

Attribute table

• CSV
  • as discussed earlier in presentation.
• Spreadsheet software like Excel, Pages, and OpenOffice can export CSV files.

Vector data

• Shapefiles are common.
• GeoJSON is text-based format.
• Mapping software uses databases (take GEO309)

Shapefiles

• Developed in the 90s by mapping company, ESRI
  • Initially proprietary but was reversed engineered.
• Stores points, lines, OR polygons (not in the same file).
• Contains table of attributes.
• Multiple files with the same name but different extensions.

Shapefile format

• Like a basketball team, each file has a different role and must play together.
• .shp stores geometry
• .dbf contains attributes
• .prj explains the coordinate system
• Many others (.shx, .sbn, .sbx, .fbn, etc.) provide additional information.

🔎 Shapefile gotchas

• All files must be in the same folder.
• Manage them as a team.
• Do not edit the files outside of GIS software.

GeoJSON file

• Open-source standard for web mapping.
  • Geographic JavaScript Object Notation
• Stores points, lines, AND polygons (in the same file).
• Can contain tabular attributes.
• Single file with .geojson extension and editable in text editor.

🔎 GeoJSON gotchas

• If you edit the file in a text editor, make sure not to:
  • change the order of the coordinates.
  • Delete or add a comma, brackets, or quotes.
  • Reserved characters: , {} [] ""

Raster data

• GeoTIFF is common.
• Mapping software uses databases (take GEO409 and GEO419)

GeoTIFF file

• Common open-source raster file format
  • Georeferenced Tagged Interlaced File Format
• Only edit in GIS software.
• Single file with .tif extension (sometimes might have companion .tfw file).
• Download example file.

Point cloud data

• LAZ most common.

LAZ file

• A zipped (compressed) LASer file.
• Single file with .laz extension.
• Download example file. (It might crash QGIS!)