A Gentle Introduction to GIS (PyCon 2012)

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PYCON 2012 A GENTLE INTRODUCTION TO GIS Jason Scheirer esri bit.ly/pycongis

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Front Matter Things I wish I’d known Lots of theory The web is already covered bit.ly/pycongis

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More than points

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More than points

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More than points

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More than points

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More than points

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More than points

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Storage

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Vector Data FILE Shapefile KML GML GPX GeoJSON Spatialite File GDB (Esri) DATABASE SQL Server Oracle PostGIS

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Raster Data FILE GeoTIFF JPEG2000 Esri GRID NetCDF HDF5 IMG ECW MrSID File GDB (Esri) DATABASE SQL Server Oracle PostGIS

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Data is conventional

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Constraints are not Integrity = Topology

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COPY/CONVERT/TRANSLATE/REPROJECT ogr, pyproj ogr2ogr, gdalwarp, gdaltransform, gdal* arcpy.management.CopyFeatures arcpy.management.CopyRaster arcpy.management.Project arcpy.management.DefineProjection OSS: ArcGIS:

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What

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Perfect sphere

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Lumps and bumps

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Tweak to fit

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Just a little more...

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Close enough!

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Geodesy

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WGS 84 Global Positioning System datum

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NAD 83 North American datum

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DEGREE/MINUTE/SECOND 17°39'27"E 14°42'33"N DECIMAL DEGREES 17.6574318720082 14.7092630700184 UTM ZONE 33P 1627845N 786174E

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UTM ZONES

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UTM GRID

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UTM GRID

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U.S. STATE PLANE !

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Geographic Coordinate Systems Global Degrees Regional UTM Zones Local Grids/Planes

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Visualization

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f(x, y, z) (x, y) Map Projection

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Mathematical model of planet/area of interest Datum/Grid/Benchmark Context for referring to places on model Geographic Coordinate System Mapping from geographic to map coordinates Projected Coordinate System Map

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The big tradeoff Preservation of shape Preservation of area

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Every map is a LIAR

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Great Circle

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>>> geod = pyproj.Geod(ellps='WGS84') >>> geod.npts(-116.993, 36.404, -0.659, 53.501, 10) [(-111.95067424159357, 41.97895680147041), (-105.96857250647616, 47.28567205186159), (-98.70968905555657, 52.20795019303087), (-89.76321873473009, 56.57373830261407), (-78.73417693105489, 60.137140502912196), (-65.50792704328728, 62.583294153845756), (-50.664741106486275, 63.59986753968315), (-35.59231296246254, 63.024821865584016), (-21.813955926298505, 60.952490703845044), (-10.156489980662073, 57.66944410754948)]

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>>> sr = arcpy.SpatialReference("WGS 1984 World Mercator") >>> start, end = (arcpy.Point(-116.993, 36.404), arcpy.Point(-0.659, 53.501)) >>> polyline = arcpy.Polyline(arcpy.Array([start, end]), sr) >>> [polyline.positionAlongLine(polyline.length * (idx / (11.))) for idx in xrange(12)] [, , , , , , , , , , , ]

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Analysis

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Doing stuff with spatial data

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Geocoding 480 New York St, Redlands, CA Art Galleries near 92373 White House

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Network Analysis Right on... Left on... Currently there are 15 households without power...

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Spatial Analysis Relational Topological

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Relational operators Contains Indicates if this geometry contains the other geometry. Crosses Indicates if the two geometries intersect in a geometry of lesser dimension. Disjoint Indicates if the two geometries share no points in common. Negate this result to compute the Intersect relation. Equals Indicates if the two geometries are of the same type and define the same set of points in the plane. Overlaps Indicates if the intersection of the two geometries has the same dimension as one of the input geometries. Touches Indicates if the boundaries of the geometries intersect. Within Indicates if this geometry is contained (is within) another geometry.

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Relational operators NOT DISJOINT

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Topological operators Boundary The boundary of this geometry. A polygon's boundary is a polyline. A polyline's boundary is a multipoint. A point or multipoint's boundary is an empty point or multipoint. Buffer Constructs a polygon that is the locus of points at a distance less than or equal to a specified distance from this geometry. Convex Hull Constructs the convex hull of this geometry. Cut Splits this geometry into a part left of the cutting polyline, and a part right of it. Difference Constructs the geometry containing points from this geometry but not the other geometry. Intersect Constructs the geometry that is the set-theoretic intersection of the input geometries. Use different resultDimension values to generate results of different dimensions. Symmetric Difference Constructs the geometry that contains points from either but not both input geometries. Union Constructs the geometry that is the set-theoretic union of the input geometries.

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Topological operators

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Topological operators

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Topological operators

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Topological operators

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Topological operators

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Topological operators

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Topological operators

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Intersect/not disjoint (ArcGIS) sr = arcpy.SpatialReference("WGS 1984 World Mercator") with arcpy.da.SearchCursor('fastfood.shp', 'SHAPE@' spatial_reference=sr) as cursor: buffered_points = [row[0].buffer(1000) for row in cursor] with arcpy.da.SearchCursor('schools.shp', ['SHAPE@', 'school_name']) as school_cursor: schools_within_1k_of_fast_food = [row[1] for row in school_cursor if any(not shape.disjoint(pt) for pt in buffered_points)] buffer_dataset = arcpy.analysis.Buffer('fastfood.shp', r'in_memory\buffered_points', '1 kilometer') arcpy.analysis.SelectByLocation('schools.shp', 'within', buffer_dataset) arcpy.management.CopyFeatures('schools.shp', 'found_schools.shp') arcpy.management.Delete(buffer_dataset)

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gis.stackexchange.com bit.ly/pycongis Basemaps used: Light Gray Canvas, World Topo, National Geographic World Map. All on ArcGIS Online.