Categorical Line Chart with Gridlines

<!DOCTYPE html>
<meta charset="utf-8">
<title>Categorical Line Chart with Grid guildlines</title>
<style>
.d3-tip {
  cursor:pointer;
  line-height: 1;
  font-weight: bold;
  padding: 12px;
  background: rgba(0, 0, 0, 0.7);
  color: #fff;
  border-radius: 2px;
}
/* Creates a small triangle extender for the tooltip */
.d3-tip:after {
  box-sizing: border-box;
  display: inline;
  font-size: 10px;
  width: 100%;
  line-height: 1;
  color: rgba(0, 0, 0, 0.7);
  content: "\25BC";
  position: absolute;
  text-align: center;
}
/* Style northward tooltips differently */
.d3-tip.n:after {
  margin: -1px 0 0 0;
  top: 100%;
  left: 0;
}
.axis path,
.axis line {
  fill: none;
  stroke: #ddd;
  shape-rendering: crispEdges;
}
.x.axis path {
	stroke : #000;
}
.line {
  fill: none;
  stroke: steelblue;
  stroke-width: 1.5px;
}
</style>
<body>
<div id = "line"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.17/d3.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3-tip/0.6.8/d3-tip.min.js"></script>
<script>
	var div = "#line"
	var grid =  true, 
		Y_AXIS_LABEL = "Frequencies", 
		main_height = 400, 
		lineType = "cardinal",
		yFormater = d3.format(",.2s"), 
		textRotate = "-65", 
		rotation = true,		
		xCategories = "State"; 
	var legend_width = 120; 				
	var color = d3.scale.category10();	
		
	var mainWidth = 900;
	var margin = {
			top: 20,	
			right: 20,	//80, 	
			bottom: 40,	//120,	
			left: 120	//50 
		},
		width = mainWidth - margin.left - margin.right-legend_width,
		height = main_height - margin.top - margin.bottom;
	var x = d3.scale.ordinal().rangeRoundBands([0, width], 1),
		y = d3.scale.linear().range([height, 0]),
		xCircle = d3.scale.ordinal();
	
	d3.json("population.json", function(data){ 
	data.sort(function(a, b){
		if(xCategories == "date"||xCategories=="Date"){
			a = a[xCategories].split("-");
			b = b[xCategories].split("-");
			var ad = new Date(a[2], a[1], a[0]);
			var bd = new Date(b[2], b[1], b[0]);
				return ad - bd;
		}else{
			return a[xCategories] - b[xCategories];
		}					
	});
	if(grid){
		var xAxis = d3.svg.axis().scale(x).orient("bottom").innerTickSize(-height).outerTickSize(0).tickPadding(10),
		yAxis = d3.svg.axis().scale(y).orient("left").innerTickSize(-width).outerTickSize(0).tickPadding(10).tickFormat(function(d){ return yFormater(d); });
	} else{
		var xAxis = d3.svg.axis().scale(x).orient("bottom"),
		 yAxis = d3.svg.axis().scale(y).orient("left").tickFormat(function(d){ return yFormater(d); });
	}	
	//color.domain(d3.keys(_this.data[0]).filter(function (key) {
	color.domain(d3.keys(data[0]).filter(function (key) {
		return key !== xCategories;
	}));
	var cities = color.domain().map(function (name) {
		return {
			name: name,
			values: data.map(function (d) {
				return {
					key: d[xCategories],
					Value: +d[name],
					color: name
				};
			})
		};
	});
	var line = d3.svg.line()
		.interpolate(lineType)
		.x(function (d) {
			return x(d.key);
		})
		.y(function (d) {
			return y(d.Value);
		});
	d3.select(div).select("svg").remove();
	var svg = d3.select(div).append("svg")
		.attr("width", width + margin.left + margin.right+legend_width)
		.attr("height", height + margin.top + margin.bottom)
		.append("g")
		.attr("transform", "translate(" + margin.left + "," + margin.top + ")");
		
	var tip = d3.tip()
		.attr('class', 'd3-tip')
		.offset([-10, 0])
		.html(function (d) {
			
		 return "<center><span>"+xCategories+" : "+d.key+"</span><br /><span>"+d.color+" : "+yFormater(d.Value)+"</span></center>";
		});
	svg.call(tip);
	var yMin = d3.min(cities, function (c) {
		return d3.min(c.values, function (v) {
			return (v.Value);
		});
	});
	var yMax = d3.max(cities, function (c) {
		return d3.max(c.values, function (v) {
			return v.Value;
		});
	});
	var d_f = (yMax - yMin)/8;
	yMin = yMin - 2*d_f;
	yMin = yMin < 100000 ? yMin : 100000;
	x.domain(data.map(function (d) {
		return d[xCategories];
	}));
	y.domain([yMin, yMax]);
	xCircle.domain(data.map(function (d) {
		return d.name;
	}))
		.rangeRoundBands([0, x.rangeBand()], 0);
	if(rotation){
	svg.append("g")
		.attr("class", "x axis")
		.attr("transform", "translate(0," + height + ")")
		.call(xAxis)
		.attr("stroke-width", "1.5px")
		.selectAll("text")
		.style("text-anchor", "end")
		.attr("dx", "-.8em")
		.attr("dy", ".15em")
		.attr("transform", function (d) {
			return "rotate("+textRotate+")"
		});
	} else {
		svg.append("g")
			.attr("class", "x axis")
			.attr("transform", "translate(0," + height + ")")
			.call(xAxis)
			.attr("stroke-width", "1.5px")
			.selectAll("text")
			.style("text-anchor", "end");
	}
	svg.append("g")
		.attr("class", "y axis")
		.call(yAxis)					
		.attr("stroke-width", "1.5px")
		.append("text")
		.attr("transform", "rotate(-90)")
		.attr("y", 6)
		.attr("dy", ".71em")
		.style("text-anchor", "end")
		.text(Y_AXIS_LABEL);
	var city = svg.selectAll(".city")
		.data(cities)
		.enter().append("g")
		.attr("class", "city");
	city.append("path")
		.attr("class", "line")
	// .attr("transform",function(d){ return "translate(" + xCircle(d.date) + ")"; })
	.attr("d", function (d) {
		return line(d.values);
	})
		.style("stroke", function (d) {
			return color(d.name);
		})
		.attr("stroke-width", "1.5px");
	city.selectAll("circle")
		.data(function (d) {
			return d.values;
		})
		.enter()
		.append("circle")
		.attr("r", 5)
		.attr("cx", function (d) {
			return x(d.key);
		})
		.attr("cy", function (d) {
			return y(d.Value);
		})
		.style("fill", function (d) {
			return color(d.color);
		})
		.style("stroke", "none")
		.style("pointer-events", "all")
		.style("cursor", "poiter")
		.on("mouseover", tip.show)
		.on("mouseout", tip.hide);
		
	var legend = svg.selectAll(".legend")
				.data(color.domain().slice().reverse())
			  .enter().append("g")
				.attr("class", "legend")
				.attr("transform", function(d, i) { return "translate(0," + i * 20 + ")"; });
			legend.append("rect")
				.attr("x", width - 18+legend_width)
				.attr("width", 18)
				.attr("height", 18)
				.style("fill", color);
			legend.append("text")
				.attr("x", width - 24+legend_width)
				.attr("y", 9)
				.attr("dy", ".35em")
				.style("text-anchor", "end")
				.text(function(d) { return d; });
				
	});
</script>
</html>

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

https://cdnjs.cloudflare.com/ajax/libs/d3-tip/0.6.8/d3-tip.min.js