I was wondering if it were possible to extract coordinates from a static map picture like this:
Is it possible to extract the coordinates of the routes? The only idea I can come up with, other than manually getting them by hand, is by overlaying the map and extracting the exact coordinates that way.
The process that you are looking for is called georeferencing in a GIS context.
In order to determine the latitude/longitude coordinates of a point (or series of points in a line), you need to first establish coordinates of other known points. These are reference points of known locations (such as a distinctive coastline, or a city). Applying these to the raster image that you have, you can then overlay it on a map in a GIS application and then query other unknown locations on the image (such as the routes) to establish their latitude/longitude.
You could attempt this in a graphics program by looking at the x/y coordinates of the route pixels and compare to a known reference point pixel; however, the math on that is going to be tedious and you also wouldn't account for the map projection. Both of those are taken care of by georeferencing.
I would note that you should consider the results you get, even in a well-referenced GIS, to be approximate. The map deals with a very large spatial area, and the routes cover long distances. But since it dates from 2012 it was presumably made in a GIS application and so at least the source data is likely to be accurate :)
Additional resources:
Help Page for ArcGIS (both overview and instructions)
Help Page for QGIS (tutorial)
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I'm interested in implementing some data visualizations as map layers. But I'm interested in generating data layers only above land area (land cover). A good example would be to plot population density over a coastal city. What is a good approach for this, when it comes to the data source and how to actually display layers with such detailed boundaries?
Technically, so far I'm using Leaflet.js and tiles based on OpenStreetMaps, but the question is not necessary technology specific. Also, I'm not interested in plotting this for the whole planet, but for areas of a few hundreds square kilometers (for e.g. a coastal city).
To better give an idea of what I'm interested in, this Koordinates map is something that is similar to what I'm interested in. However, I need something a bit more detailed on the borders.
Usually you need a desktop or server based GIS such coverage, but not JS to do the processing on the client side.
How you do the mapping (here: linking statistical data and land areas) depends on your data itself. You can load OSM based shape files into QGIS and do some python scripting or using the PostGIS commands to link your data and choose a map style.
Another idea would be http://geocommons.com that allow easy visualization if you upload CSV files.
Depending on your area of interest, you can obtain some highly detailed shapefiles from numerous sources. Especially if the local area provides GIS data to the public (many larger coastal cities do, e.g. New York, London). From there, you can create a GeoJSON text of the geometries (here's a free tool for that). Parsing the JSON is very simple and it's very easy to add it to leaflet maps. You can even get creative and add more keys to each geometry object with the data you want to visualize.
I'm trying to build a map with the following algorithm:
Wait for pan or zoom to occurs.
Query for all streets visible in the viewport (extent).
Color every visible street with a predefined color.
Example:
I want to show the numbers of businesses on each street, or the number of crimes committed at each street.
I have a DB which holds this kind of information (streetname, data), but each row doesn't have the location data.
Therefore, after each map zoom or pan, I cannot query all of it by a geographical bounding rectangle, it will be far more efficient to use Google own DB and query it by street names.
I know how to register to pan and zoom events.
I know how to calculate the viewport coordinates.
I know how to color a single street.
How can I get a list of all streets visible in the viewport?
Any other solutions or architectures are welcome.
The preferred solution will not use Google DirectionsService nor DirectionsRenderer since they slow down the map.
My understanding is that what you are asking is not possible from Google API's. Reverse geocoding inside a polygon is not a service they offer. There are some posts on other sites (e.g. https://gis.stackexchange.com/questions/22816/how-to-reverse-geocode-without-google) with the reference gisgraphy.com looking like a pretty neat reverse geocoding tool.
This still does not address your all streets in a polygon problem however. I think your only option would be to get your hands on the data (Open Street Maps) and write the code yourself. Further - if you are going to do this for a large area I would take an approach like I recommended here with grids: https://stackoverflow.com/a/18420564/1803682
I would create my grid elements, and for each street calculate all the grids to which it belongs and store in the database. Then when you search a polygon, you would calculate all the grids the polygon overlaps, and can then test the subset of road data in each of those squares to determine overlap.
I looked into this and abandoned a similar requirement a few months back and still have a desire to implement it. Most of the point/line in polygon work is happening on data created in my application (i.e. not street data) and right now that is the only data I will be including. What I am trying to say is - I hope someone gives you a better answer.
Update:
For what you are asking I still believe you will need to use a mix of your own database based on OpenStreetMap and some kind of grid analysis carried out in advance. If you have some time to commit to the project this should not be too awful to process. The database will be large, and the calculations needed will likely require a significant amount of one-time / upfront processing time. As far as highlighting routes/roads/whatever within the viewport, there are lots of way to accomplish this using the API - example here which I found useful: polyline snap to road using google maps api v3
Also useful: http://econym.org.uk/gmap/snap.htm
Note that one way streets may give some grief if using the directions api to snap to a street and you will likely have to watch for this and correct or reverse the start/end points.
Google would recommend using it's Geocoding Service in order to populate your data base with the co-ordinates. You can then use the LatLng Bounds Class method "contains" to check whether your points lie within the viewport. The advantage of this approach is you only need to geocode the information once and then store this, versus sending coding requests each time the viewport changes.
An alternate efficient way of displaying this kind of data may be to use google fusion tables. this greatly simplifies the integration of the data with the map.
I would like to have the possibility to tell if a GPS location is in an inhabited or uninhabited zone.
I have tried some reverse geocoding services out there, but all of them proved useless, because they select the nearest address possible. (I understand why this should be so, it is useful for the purpose of reverse geocoding)
I have noticed in Google Maps, when I search for a city, their boundaries are selected in red dotted well defined line. I would love it to use this, or something similar.
Is there any possible way that Google maps can provide such a service, or something that can solve my problem.
Are there any other web solution or databases that you know of that can give me this information ?
Or maybe I can use any of the reverse geocoding solutions with some parameters (such as restricting the size of searching) to determine if the location is or is not in a populated area?
If you will not find a public service then it gets interesting, and expensive in terms of developping effort.
Public data (world wide) is only available from OpenStreetMap, i think they have such a layer (could be named Land_use (rural, etc.)) This layer is usually used to color a map, look at openstreet map Web page if you find a suitable coloring, that coresponds to your task. (E.g look at green, or gray).
These data are stored in polygons, you would have top extract these polygons (i asume millions of them). Ten you need a fast searching spatial index, like a region Quadtree.
Then you do a "point(lat, lon) in polygon" call, and get the polygon related to your position.
Probaly not all that polygons will fit into main memory, so you must load them on demand (e.g by country).
A variant of this approach is to use a geo spatial database like postgres to store that polygons, and do a DB query.
With that approach most work will be extracting the polygons from OpenStreetMap DB file.
More acurate is data from TomTom, but these can be really expensive.
I have an application that draws a vector map of the 50 United States. Each state is a polygon. These polygons change color as the state of the application changes.
I obtained the coordinates I'm using now by laboriously tracing a scanned in map with a mouse, recording the screen coordinates as I did so. As you can imagine my vector map is pretty ragged. I'd like improve the appearance of my maps by using real boundary coordinates for each state, and in the future use other political boundaries in my app such as counties or congressional districts.
I know nothing about GIS systems, nothing at all. I do think that given a vector of lat/long pairs for the borders of each political entity I could convert the lat/longs into screen coordinates. I used to be an Air Force navigator, so I'm comfortable with lat/long calculations.
Bottom line: I need an open source or public GIS database system that could spit out a list of Lat/Long pairs for the boundaries of the fifty States.
Can someone provide a pointer to such a database and hopefully a tutorial of some kind describing how to extract political boundary information from it?
Thanks in advance!
The Census Bureau provides the TIGER data sets that include shapefiles for state outlines (and much, much, more). The downloads are in ESRI Shapefile format, which can be opened by most GIS applications, such as the easy to use open-source QuantumGIS. To convert the shapefiles to a format that's easier to work with, see this question. Once you've got the vector data into your program, you'll probably realize that it's more detailed than you want. Check gis.stackexchange.com for some tools to simplify the polygon outlines. Once you've got the sets of points you want, you may want to use the PROJ library to handle the projection of the points on to your map.
I am trying to take a shapefile of subdivisions within a county that I have created and line it up with another shapefile that was given to me by the County Appraisal District (parcel data). When I try to get them to line up then my streets shapefiles is not aligned with everything else. They are all on the same coordinate system and I do not want to have to recreate the shapefile for the subdivisions. Any thoughts?
This is a question with answers that may be simple or may be very complex, depending on your situation. As a GIS developer, I've most commonly seen this as a symptom of an incorrectly defined coordinate system. However, whether this is the case or not, and what the solution is strongly depends on your environment. From here on, I'll assume that you're working in an ESRI package...
I agree with the other posters that your problem is one of mismatching projections and/or datum definitions.
The most important thing to understand as regards projections in ESRI software is this:
Manually setting the projection of a dataset (shapefile, geodatabase feature class, etc) in ArcCatalog does NOT reproject that dataset!!!
In order to reproject your data, you must EXPORT the data from an ArcMap session in which you've been working and where the data is obviously lined up correctly. During the EXPORT, you are given the choice of saving your data with the coordinate system of the underlying map or that of the original dataset.
Your best bet is to follow these steps to create a new dataset with the correct projection and then extrapolate what you need to do to fix your specific problem:
Create a new ArcMap session and set its coordinate system:
Do this in a fresh ArcMap session with NO OTHER DATA. Be sure to explicitly set the coordinate system of the ArcMap mapview to your desired coordinate system (I recommend the one that matches the data you're trying to overlay, or one from another well-established dataset).
Add one other dataset with a known good coordinate system.
Create your new dataset in this ArcMap session. Give your new data the same coordinate system as the ArcMap mapview and the one other dataset in the map. Set the XY domain of the new data to exceed the area defined by your other dataset, but don't go beyond the size that will reduce your desired spatial resolution.
Create your data. It can be any data at this point. Some lines, some polygons, etc. Save your work.
Export your new dataset. When prompted, choose to save with the coordinate system of the underlying mapview.
Create a new ArcMap session and add your new dataset. Then add your parcel dataset. They should now occupy the same space in your map window.
Edit your new data to your heart's content.
Some probable issues if this doesn't help:
You didn't follow these steps correctly - check the ESRI documentation; this is a well documented issue.
The parcel data you're trying to match doesn't have properly defined coordinate system. It's always possible that the keepers of this data don't know what they're doing and have munged it up. I've seen this problem more times that I care to admit.
You've matched the projection but have mis-matched the datum. Many municipalities are still using data in NAD27, which is way out of date. Some have moved to the modern NAD83. The difference can be up to 300 meters, depending on where in the country you are. Also, data that originates from surveying or GPS equipment is usually collected in WGS84 (the typical default for satellite surveying), which is for all practical purposes the same as NAD83, at least at mapping scale resolutions.
Try researching these issues and see how it goes. I'll say it again:
Manually setting the projection does NOT actually project that data!!
Good luck!
Your problem is probably one of projection
| projection: character string that names a map projection to use. See
| 'mapproject' (in the 'mapproj' library). The default is to
| use a rectangular projection with the aspect ratio chosen so
| that longitude and latitude scales are equivalent at the
| center of the picture.
`-----
Agree that your problem is projection. Is there a .prj file extension associated with either of your files? If not key first is finding out what projects you have. I would guess State Plane of some sort if you are dealing with U.S. centric local data from a local government.
Cadastral tools (surveyer tools) usually let you specify a handful of control points and will then "warp" the data to fit to your control points. This can be anything from a simple shift to something more complex. If everything is shifted by a few feet, you can also just use your "editor" to select all shapefiles and then move them however many feet necessary.
If you've verified that both shapefiles are using the same coordinate system, then projection is less likely to be the problem. It's fairly common for parcel data to be "offset" from other data sources (such as roads). This comes from inconsistent collection methods and points of reference.
Another source of error can be that one of the shapefiles has the wrong coordinate system specified. For example, if the roads were actually WGS 1984, but it's prj is set to NAD1983, you will see some significant errors. This usually happens if you had to manually set the coodinate system for a shapefile (i.e. it didn't include a PRJ and you created one).