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Monthly Archives: April 2010

Avenza State Plane Coordinate System Map

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MAPublisher and Geographic Imager provide an extensive library of predefined coordinate systems available for referencing or transforming mapping projects.

In the United States, the NGS (National Geodetic Survey), a department of NOAA (National Oceanic and Atmospheric Administration) has established a system that divides the United States into 124 zones, each with its own custom projected coordinate system. This system is known as the State Plane Coordinate System. It is important to note that there are two sets of State Plane coordinate systems defined in the United States, one based on the North American Datum of 1927 and the other based on the North American Datum of 1983. In addition to NAD 83, the NAD83 HARN and NSRS2007 adjustments are available for use. All three versions of NAD83 are available in metres, feet or international feet.

State Plane Coorindate Systems projections

There are four projections for SPCS. The geometric direction of each state determines the projection utilized. For states that are longer in the east-west direction, the Lambert Conformal Conic is used. States which are longer in the north-south direction use the Transverse Mercator projection. The panhandle of Alaska, which has the sole distinction of lying at an angle, garners the use of the Oblique Mercator projection, while Guam uses a Polyconic projection.

These coordinates systems are all defined in the MAPublisher and Geographic Imager library, however the initial question “which one do I need to use for my map” cannot be answered by the software itself.

There are a number of ways to determine in which zone your American area of interest lies. One online resource, searchable by latitude and longitude coordinates, can be found on this NGS website.

In an effort to better assist mapmakers in their selection of the appropriate system, the Avenza support team has prepared a searchable interactive map using MAPublisher 8.2 MAP Web Author tool. View the SPCS map here.

A MAPublisher geospatial PDF of the same map is also available for download here.

Transform into State Plane Coorindate Systems using MAPublisher

When it comes time to transform your data into the appropriate State Plane Coordinate System zone, use the MAP View Editor Perform Coordinates System Transformation option. When you specify the destination coordinate system for the transformation, navigate to Coordinate Systems > Projected > North America > United States > US State Plane NAD 83 – on the right hand list, you’ll find all the state plane zones sorted by state name and zone name: select the right one!

Note: similarly you can select the NAD27 state plane systems from Coordinate Systems > Projected > North America > United States > US State Plane NAD 27 if appropriate.

Improved Reprojection Engine in MAPublisher 8.3

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One of the exciting new changes in MAPublisher 8.3 is that we’ve substantially rewritten our reprojection engine. What I’d like to do here is explain what the changes are, and what they mean for you, the user.

The old reprojection engine was point-by-point. Essentially, we walked each path and simply reprojected each point one by one. This simple approach works very well but it has one important deficiency: it lacks context. The internal reprojection system never sees anything more than a single point, and therefore is limited to just reprojecting.

So what is the new system doing? Our new reprojection engine is performed feature-by-feature. This is important because it means the internal system no longer just sees a single point, but rather a collection of points and how they are arranged. This means it can notice things like an area that wraps around to the other side of the world! In the old system, it would just blindly punch out points, and if a path suddenly jumped to the other side of the page, well, that’s where the path went. But now the reprojection engine can notice things like that, and clip the art appropriately. If necessary, it will even break a single path into a compound path! But it’s probably easier to understand if we demonstrate it visually.

Here is a map of Canada with two layers: rivers & provinces. Both sets of art are coloured nicely and the provinces layer even has an opacity reduction to make the rivers stand out a little.

Before transform

I’ve created a new coordinate system I’ve called ‘Miller Cylindrical Shifted’. I just made a copy of the ‘Miller Cylindrical’ coordinate system and then altered my copy’s central meridian to be 90 instead of zero. I did this so that if I reproject Canada into ‘Miller Cylindrical Shifted’, half of Canada should be on the left-hand side, and half should be on the right-hand side. Let’s see how MAPublisher 8.2 handles it:

After transform in 8.2

Yikes! The old reprojection engine had no idea that some of those lines were going off the end of the projection’s envelope!

Now let’s try it in MAPublisher 8.3 with the new reprojection engine:

After transform in 8.3

Wow! What a difference feature-by-feature makes! The new engine recognizes that those paths needed to be clipped and properly split polygons and lines as needed. It’s also important to note that the areas & lines are still intact. e.g. Northwest Territories was split, but it’s still a single compound path with all of its islands — some of those islands have simply been split into pieces. The split even preserves all the original path’s properties, including attributes and styles!

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