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alexmacy

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OPD License Plate scans

I'm a big fan of locations and patterns, and particularly social patterns relating to location, movement, and usage trends. I'd been looking for a way to explore this when I heard about the Oakland Police Department having released all their license plate reader data.

I filtered this data to license plates that appeared in a minimum of 15 distinct locations, and then removed obvious errors (like 'CAUTION' and other street signs) as well as government vehicles like buses and police cars (these have numeric digits only, rather than the alpha-numeric). The result was 205 plates, with 6,623 unique scan events.

It's not really enough data to find trends, but it was a good exercise in learning mechanisms that can be used to find and rank common traits. For this, I compared the locations that each license plate had been scanned and calculated the similarity to the other license plates. This was done by looking at the co-occurance of the geographic coordinates after having rounded them to two decimal points.

On load, each scan event is displayed as a SVG path, and a list of all the license plates is created on the left side. Hovering over this list and/or clicking on a license plate displays only that plate's events. This also compares this plate's events to teh events of all the other plates and returns a list of the 30 most similar plates on the right side of the window. Hovering over the list of compared license plates (or clicking on one) displays the compared plate's events as blue markers.

Alternatively, you can click on a marker and the list on the left will scroll to that plate and display it's other events.

<!DOCTYPE html>
<html lang="en">

<head>
    <title>opd_lpd_leaflet</title>
    <meta charset="UTF-8">
    
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/leaflet/0.7.7/leaflet.css"/>

#map {
            position: absolute;
            width: 100%;
            height: 100%;
        }

.side-container {
            position: absolute;
            z-index: 5;
            width: 8%;
            max-height: 83%;
            margin-top: 6%;
            padding: 5px;
            border: 1px solid black;
            border-radius: 5px;
            background-color: rgba(255, 255, 255, .9);
            overflow-y: auto;
            overflow-x: hidden;
        }

.count-container {
            position: absolute;
            z-index: 5;
            width:20%; 
            margin-top: 10px;
            margin-left: 40%;
            padding: 5px;
            border: 1px solid black;
            border-radius: 5px;
            background-color: rgba(255, 255, 255, .9);
        }

.selected {
            background-color: lightblue;
            font-size: 20px;
            font-weight: bold;
        }
        
        .hovered {
            font-size: 20px;
            font-weight: bold;
        }

.d3-tip {
            line-height: 1;
            padding: 12px;
            background: rgba(10, 10, 10, 0.9);
            color: #fff;
            border-radius: 5px;
        }

</style>
</head>

<body>

<div id="master-list-container" class="side-container" style="left:10px;visibility:hidden;text-align:left;">
        <div id="master-list"></div>
    </div>
    
    <div id="compare-list-container" class="side-container" style="right:10px;visibility:hidden;text-align:right;">
        <div id="compare-list"></div>
    </div>
    
    <div id="count-container" class="count-container" style="visibility:hidden">
        <span class="col-sm-8" id="count-span" style="text-align: right">
            <span id="count"></span> of <span id="count-total"></span> events visible
        <button class="col-sm-9" type="button" onclick="showAllMarkers();" style="float:right;margin-top" >Show All</button>
    </div>

</body>

//to store the data imported by d3.json
	var scanData = [],
        map,
        g,markerCount;

loadMap();
    loadData();

function loadMap() {
        map = L.map('map').setView([37.80, -122.22], 12);

Stamen_TonerLite.addTo(map)

//initialize the SVG layer 
        map._initPathRoot()

//re-size/re-position the markers when the map is zoomed or moved
        map.on("viewreset", updateSVGMarkers)
    }

function loadData() {     
        d3.json('opd_lpd.json', function(error, jsonData) {

scanData = jsonData;

loadD3Markers();
            updateSVGMarkers();
            loadMasterList();
        })
    };

function loadD3Markers() {

//create a 'g' element for each license
        d3.select("#map").select("svg").selectAll('g')
            .data(scanData)
                .enter().append('g')
                //attach the license to the parent as a class for faster selecting when showing/hiding
                .attr('class', function(d) { return 'lp' + d.license })
                //create a 'path' marker for each location associated with the license plate
                .selectAll('path')
            .data(function(d) { return d.locations;})
                .enter().append('path')
                .attr('d', 'M04 16 S14 0 4 00 S4 16 4 16')
                .style("stroke", "black")  
                .style("stroke-width", "1")  
                .style("fill-opacity", .6) 
                .style("fill", "red")
                .classed('shown', true)
                .style('cursor', 'pointer')
                .call(markerTip)
                //on click, display only this license's markers and scroll the master list until it is displayed
                .on('click', function() {
                    var thisLicense = d3.select(this.parentNode).data()[0].license;
                    
                    //deselect anything currently selected in the lists
                    d3.selectAll('.selected').classed('selected', false);

//set this license as 'selected'
                    d3.select('#ml_' + thisLicense).classed('selected', true);

//hide all currently displayed markers
                    d3.selectAll('.shown')
                        .style('visibility','hidden')
                        .classed('shown', false);

//select and display markers associated with this license plate
                    d3.selectAll('.lp' + thisLicense).selectAll('*')
                        .style('visibility', 'visible')
                        .style('fill', 'red')
                        .classed('shown', true)

//scroll to specified license plate
                    d3.select('#master-list-container').transition().duration(3000).ease('cubic-in-out')
                        .tween("uniquetweenname", scrollList(d3.select('#ml_' + thisLicense)[0][0]))
                        .each("end", loadCompareList(d3.select('#ml_' + thisLicense).data()[0]));
                })
                .on('mouseover', markerTip.show)
                .on('mouseout', markerTip.hide);

//count the markers for the total to be displayed in the count-container
        d3.select('#count-total').html(d3.selectAll('path')[0].length);

}

function updateSVGMarkers() {
        //reposition the markers to their locations in relation to the map tiles
        d3.selectAll('path')
            .attr("transform", function(d) { 
                return "translate("+ 
                    map.latLngToLayerPoint(new L.LatLng(d.split(',')[0],d.split(',')[1])).x +","+ 
                    map.latLngToLayerPoint(new L.LatLng(d.split(',')[0],d.split(',')[1])).y +")";
                });  
    }

function loadMasterList() {
        //load the list for the container on the left side, sorted by number of scans
        d3.select('#master-list').selectAll('div')
            .data(_.sortBy(scanData, function(d) {return d.count}).reverse())
                .enter().append('div')
                .style('cursor', 'pointer')
                //set the id for easy finding when automating the scroll
                .attr('id', function(d) {return 'ml_' + d.license})
                .html(function(d) {return d.license})
                .on('mouseover', function(d) {
 
                    //if no line has been selected (highlighted): 
                        //hide all but the associated markers
                        //load list of the most similar license plates
                        //update the count at the top of the window

if (!d3.select("#master-list").selectAll('.selected')[0].length) {
                        d3.selectAll('.shown')
                            .style('visibility','hidden')
                            .classed('shown', false);
 
                        d3.selectAll('.lp' + d.license).selectAll('*')
                            .style('visibility', 'visible')
                            .style('fill', 'red')
                            .classed('shown', true)

loadCompareList(d)
                        
                        updateCount();
                    }

//zoom on the line in the list, regardless of other lines being selected 
                    d3.select(this).classed('hovered', true);
                })
                .on('mouseout', function() {
                    //if the line is not selected (highlighted):
                    if (!d3.select(this).classed('selected')) {
                        d3.select(this).classed('hovered', false)
                    }
                })
                .on('click', function(d) {
                    var thisRow = d3.select(this);

//toggle the selection, only one can be selected at a time
                    if (thisRow.classed('selected')) {
                        thisRow.classed('selected', false)
                        showAllMarkers(); 
                    } else {
                        d3.select('#master-list').selectAll('.selected').classed('selected', false);

//the rest of this acts like a mouseover event, but lasts until deselected
                        d3.selectAll('.hovered').classed('hovered', false)
                        thisRow.classed('selected', true);

loadCompareList(d);
                        
                        d3.selectAll('.shown')
                            .style('visibility', 'hidden')
                            .classed('shown', false);
                        
                        d3.selectAll('.lp' + d.license).selectAll('*')
                            .style('visibility', 'visible')
                            .style('fill', 'red')
                            .classed('shown', true);
                    }

updateCount();
                })

//un-hide the master list and count containers
        d3.select('#master-list-container').style('visibility', 'visible');
        d3.select('#count-container').style('visibility', 'visible');

updateCount();
    }

function loadCompareList(A) {

//check if the similarities have already been calculated
            //this is processed per select or hovered license ('A') on an as-needed basis
            //this saves time and space instead of processing through the whole list on the original load
            //the result is stored in the object so it only needs to be done once per license
        if (!A.similarities) {
            A.similarities = [];
            //it then compares the scans for each license and returns the 30 most similar licenses, sorted by similarity
            scanData.forEach(function(B, i) {
                if (A.license != B.license) {
                    var locationsA = _.uniq(A.locations.map(function(d) {
                        return [d3.round(+d.split(',')[0],2), d3.round(+d.split(',')[1],2)].join()}));
                    var locationsB = _.uniq(B.locations.map(function(d) {
                        return [d3.round(+d.split(',')[0],2), d3.round(+d.split(',')[1],2)].join()}));
                    //count the common locations and divide by the combined number of locations
                    var thisSimVal = _.intersection(locationsA,locationsB).length/(locationsA.length + locationsB.length);

A.similarities.push({
                        "license": B.license,
                        "value":thisSimVal, 
                    });
                };
            })
            A.similarities = _.sortBy(A.similarities, function(d) {return d.value}).reverse().slice(0,30)
        };

//remove any previously loaded list and replace with the new one
        d3.select('#compare-list').selectAll('div').remove();

//the mouse events are like the master list, but multiple lines can be selected and the markers are blue
        d3.select('#compare-list').selectAll('div')
            .data(A.similarities)
                .enter().append('div')
                .html(function(d) {return d.license})
                .on('mouseover', function(d) {
                    console.log(d3.format('%%')(d.value));
                    d3.select(this).classed('hovered', true);
                    d3.selectAll('.lp' + d.license).selectAll('*')
                        .style('visibility', 'visible')
                        .style('fill', 'steelblue')
                        .classed('shown', true);
                    
                    updateCount();
                })
                .on('mouseout', function(d) {
                    if (!d3.select(this).classed('selected')) {
                        d3.select(this).classed('hovered', false);
                        d3.selectAll('.lp' + d.license).selectAll('*')
                            .style('fill', 'red')
                            .style('visibility', 'hidden')
                            .classed('shown', false);
                    } 
                    updateCount();
                })
                .on('click', function() {
                    d3.select(this).classed('selected', !d3.select(this).classed('selected'));
                })

d3.select('#compare-list-container').style('visibility', 'visible');
    }

function updateCount() {
        //load a running count of the displayed markers by counting all the markers currently visible
        var shown = d3.selectAll('.shown')[0].length;
        d3.select('#count').html(shown);
    }

function showAllMarkers() {
        //reset the view to show all markers, deselect anything from the lists, and hide the compare list
        d3.selectAll('path')
            .style('fill', 'red')
            .style('visibility', 'visible')
            .classed('shown', true);

d3.selectAll('.selected').classed('selected', false);
        
        d3.select('#compare-list-container').style('visibility', 'hidden');
        
        d3.select('#compare-list-container').select('#compare-list').selectAll('*').remove();

updateCount();
    }

//tooltip for markers
    var markerTip = d3.tip()
          .attr('class', 'd3-tip')
          .offset([-10, 0])
          .html(function (d) {return d3.select(this.parentNode).data()[0].license;});

</script>
</html>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.17/d3.min.js

https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js

https://cdnjs.cloudflare.com/ajax/libs/leaflet/0.7.7/leaflet.js

https://cdnjs.cloudflare.com/ajax/libs/d3-tip/0.6.7/d3-tip.min.js