• Latitude: parallel to the equator; north is positive, south is negative • Longitude: perpendicular to the equator; west of Greenwich, England is negative, east of it is positive • Both are 0 at the “center of the world”, which is the equator north/south, and the “prime meridian”, or Greenwich, England, east/west • Resets on the other side of the world, at the antimeridian: Fiji, mainly LATITUDE AND LONGITUDE
HOW FAR BETWEEN DEGREES? • All latitude & longitude degrees are not the same distance apart. So there’s no easy formula for “how far is one degree.” • Some folks use degrees, minutes, seconds (51° 28' 38'' N)… just math. +51.477222
• GIS: Geographic Information System • OpenGIS: Open spec released by OGC consortium for web geo interop; kinda like the FIG but with less drama and for geospatial • ArcGIS: $$$ Windows desktop software everyone uses; expensive, proprietary, Windows-only, etc. • PostGIS: “Spatial and geographic objects for PostgreSQL” • WKT: “Well-known text”; representing geometry as ASCII • WKB: “Well-known binary”; WKT but blobby • GeoJSON: WKT-ish, but JSON TERMS
• Basic math and stuff in that endpoint • Restaurant longitude +- (delivery_distance / 2) • Restaurant latitude +- (delivery_distance / 2) • SELECT query example for that boundary • BUT WAIT!…. DRAWING SQUARES
• Spatial Reference Identifier—for geometries or geographies • MySQL supports over 5000 SR’s • Most common: • SRID 0 (MySQL default) just means “flat” (fine for geometry, not for geography) • SRID 4326 (WGS84) is most common; what GPSes uses • SRID 3857 is what Google Maps and Bing use SRID
• Text representation of a point: POINT(LAT, LONG),SRID • Text representation of a shape: POLYGON((LONG1 LAT1,LONG2 LAT2,LONG3 LAT3,LONG1 AT1),SRID) • Others: LINESTRING, MULTIPOINT, MULTIPOLYGON, MULTILINESTRING, GEOMETRYCOLLECTION GEOMETRY COLUMN EXAMPLES
Geometry methods that can be used for select, order, and where statements (and other things—to cover later) • ST_CONTAINS: second value is within first value • ST_WITHIN: first value is within second value • ST_INTERSECTS: two shapes intersect • ST_TOUCHES: two shapes have touching boundaries ST_* METHODS
• Centroid is the center point of this shape— technically “the intersection of all straight lines that divide the shape into two parts of equal moment about the line” • In SQL: Centroid(service_regions.shape) • Less fragile “overlaps” by using “centroid is within” CENTROIDS
• Not a “file”; more like a directory of ~10 files • .shp, .shx, and .dbf files have to be in there, but there are usually more • Designed by ESRI—sort of like the spatial equivalent of .xlsx SHAPEFILES
• Created by an Internet working group () instead of an existing shadowy monolithic organization • Easy to convert to and from GeoJSON, and viable in any modern tools GEOJSON
• GDAL (Geospatial Data Abstraction Library - https:// www.gdal.org/) • Ogr2ogr (https://www.gdal.org/ogr2ogr.html) • brew install gdal • Can convert between all geospatial file formats, and even query properties of one with a SQL-like syntax CONVERTING FILE FORMATS
• Data stored as binary; convert binary to text using ST_* methods • ST_AsText(some geometry field or content in here) • Humans are bad at reading binary, turns out ! GEOMETRY-TO-TEXT CONVERSION
• Each data point lookup needs to be fast • Embed less data; look up data when they click the point • Simpler initial list: • [{lat: 1, long: 2, name: ‘abc’}, {}, {}] MORE DATA ON POPUP
• Wicket (http://arthur-e.github.io/Wicket/sandbox-gmaps3.html) • GeoJSON by Civil Service USA (https://github.com/CivilServiceUSA/ civil-services-geojson-app) • Sequel Pro USEFUL TOOLS
mattstauffer
hato3isfriend
okada_fuutass
skrb
mode86
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htsuruo
trycycle
line_developers
oracle4engineer
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