Configuring Print Scales

The fixed scales offered in the print dialog can be set via the application configuration’s print.scales. The “Scale to fit” options are always available; when print.scales is omitted a built-in set of common scales is used.

The configuration is passed to the gm3.Application constructor in your app.js.

var app = new gm3.Application({
    mapserver_url: CONFIG.mapserver_url,
    mapfile_root: CONFIG.mapfile_root,
    print: {
        scales: [
            {scale: 50},
            {scale: 1000},
            {scale: 24000},
            {label: "1000 ft / in", metersPerPt: 4.2333}
        ]
    }
});

To offer only the “Scale to fit” options and no fixed scales, set scales to an empty array:

var app = new gm3.Application({
    mapserver_url: CONFIG.mapserver_url,
    mapfile_root: CONFIG.mapfile_root,
    print: {
        scales: []
    }
});

Each entry sets the scale one of two ways:

• scale - A 1:N ratio (e.g. 24000 for 1:24000). Simplest, and the natural fit for metric printing.

• metersPerPt - The ground distance, in meters, that one PDF point of paper represents (72 points per inch). For “per inch” scales, divide the per-inch distance by 72: 1000 ft / in is 1000 * 0.3048 / 72.

label is optional; a 1:N label is derived from the scale when omitted.

The built-in scales

When print.scales is omitted, the engineering scales below are offered. They cover the US local-government use cases discussed in geomoose/gm3#999. Set print.scales to replace the list outright with your own – for metric printing, or to reach the regional scales (1 mile per inch, 1:100000) that the defaults stop short of.

Because a foot is exactly 12 inches, every “feet per inch” scale is an exact 1:N ratio, so each can be reproduced with the simpler scale form:

Scale	scale	Typical use
1 inch = 10 feet	120	Septic evaluations and permits
1 inch = 20 feet	240	Intersection layouts, utility alignments
1 inch = 40 feet	480	Residential streets, general utility plans
1 inch = 50 feet	600	Grading plans, larger parcels, subdivision layouts
1 inch = 100 feet	1200	City-wide overviews, long right-of-way maps
1 inch = 200 feet	2400	Planning and zoning maps
1 inch = 300 feet	3600
1 inch = 400 feet	4800
1 inch = 500 feet	6000	USNG and fire maps (a 1 km square fits on letter)
1 inch = 600 feet	7200
1 inch = 2000 feet	24000	7.5 minute USGS topographic quadrangle

Note

Scales assume a basemap in meters (web mercator) and are true at the map center; like any web-mercator map, scale distorts toward the poles.