Tuesday, January 17, 2012

Mapping New York - point data

We're just about done with the basemap. While we'll eventually augment it - we'll come back later to adding things like hiking tracks in the state forest lands - I'll skip them for now because they're irrelevant to my map of the Niskayuna nature preserves.

About all that remains is to add data about points of interest (and other single-point features).
All of the data that I'm adding at this step is already in the database from the ‘new_york.osm’ file. It's all in the 'point' table.

The OSM point data is, you should forgive the expression, all over the map in terms of what it describes. In order to get it to layer correctly with other things, I've broken it out into multiple layers in the QGIS project:

  • Highway points - those for which

    upper(geometrytype("way")) IN ('POINT','MULTIPOINT')
    AND "highway" IS NOT NULL
    AND "highway" NOT IN ('bus_stop', 'crossing', 'stop_sign', 'street_lamp,
    'traffic_signals', 'traffic_signals;motorway_junction',
    'unclassified', 'yield')

    These are things like roundabouts, turning circles, and freeway interchanges. They layer right next to the roads, and have a simpleminded style sheet. (The only thing of interest is that its symbols are sized in map units rather than millimetres - I represent a traffic circle by a circle of diameter 15 m at map scale.) Eventually, I want to do better labeling for numbered interchanges, but that can wait for a version of QGIS that has highway shields.

  • A mixed bag of features that includes schools, houses of worship, hospitals, public toilets, miscellaneous buildings, helipads, gates, and boat launches. (I expect this list to expand over time, depending on what is relevant to a given map. There are dozens of things that might be included.)

    upper(geometrytype("way")) IN ('POINT','MULTIPOINT')
    AND place IS NULL
    AND highway IS NULL
    AND (amenity IS NULL OR amenity NOT IN ('fire_hydrant'))

    This layer goes above the building footprints.

  • Place names (and names of dams, which are shown the same way). This layer is topmost in the stack. Its style displays nothing. It merely exists as a place for the labeling engine to add the names of objects.

    "place" IN ('city', 'hamlet', 'island', 'islet', 'locality', 'suburb',
    'town', 'unincorporated_area', 'village')
    OR "waterway" IN ('dam')

With all of this in place, the map appears quite informative - except that it's missing one of the preserves that I want to show! (The Mohawk River State Park, formerly the Schenectady Museum Nature Preserve.) In the next installment, I'll try to get that on the map.

In the meantime, here are the style sheets for the layers I discussed in this lesson:

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