How to find the coordinate system of a layer in ArcGis 10.X?

Usually, all layers of geographic data have the description of the coordinate system. Unfortunately, this is not always the case. In general, the problem greatly increases with the fact that, usually, it is quite (or completely)impossible to contact the producer of the data.

Diagnosis of the problem

 A- You ask Arcmap to load the layer and you see a warning message: The following added data sources do not have spatial reference information. This data can be displayed in ArcMap, but it cannot be projected.
If it is a layer of vector data (points, lines, polygons), the data must lack a defined coordinate system. In the case of shapefiles, the PRJ file is missing.

B- You ask Arcmap to load the layer and, without having any warning or error message, you do not see your new data or, else, they are not where they should be.
If it’s a vector data layer (points, lines, polygons), the data has a defined coordinate system, but it’s wrong. The PRJ file exists, but its contents are wrong.

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Geometry validation tools (5) with QGis

In previous articles, we have discussed the geometry validation tools with ArcGis,Spatialite / Postgis, FME and Geomedia. We still have to discuss this feature with QGis. You will see, it is not easy to find it!

 First observation: the documentation does not exist (not yet?). Therefore you have to go through tests and see what happens.

Second observation: QGis proposes two tools for verifying geometries. This is not necessarily a problem, except that the results are not the same.

So, let’s start by discussing the available tools.

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Geometry validation with QGis 2.12.0

We have already discussed the geometry validation in a series of
articles. Particularly, you can read the article The  geometry validation  tools (5) with QGis for the validation tools with
QGis 2.8

Version 2.12 brings a new plugin that changes the game. Here is a list
of  those main characteristics .

Firstly, let’s see what does not change: there is no documentation regarding
the tools used by the plugin. It is true that in order to develop those tools implies
a very hard job, but using a tool without knowing what is actually done is not
very reassuring .

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Geometry validation tools (4): Intergraph Geomedia

Wondering why discussing Intergraph Geomedia? It is true that in France
it has an almost confidential diffusion. But it does not deserve this. Besides the
fact that it has been the forerunner in many fields (the Esri geodatabase is
only the Intergraph Warehouse updated for Esri, but 10 years later), regarding
our interest, it is the proof that a lot more can be done when we really want. Let’s
see how geometry validation works with Geomedia 2014.

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Geopackage format and QGis 3

An open format for geospatial information

GeoPackage is a compact, portable, self-descriptive and open,
standards-based, platform independent and allowing geospatial information transfer

The GeoPackage standard is composed of a set of conventions to store in
a SQLite database the following items:

  • vector entities
  • matrixes from images and rasters tiles with different scales
  • attributes (non-spatial data)
  • extensions

To put it clearly, a GeoPackage is the SQLite container and the encodingstandard, GeoPackage governs the rules and requirements of the content stored in a GeoPackage container. The GeoPackage standard defines the diagram of a GeoPackage including table definitions, assertions of integrity, format limitations and content constraints. Thecontent required and taken in charge of a GeoPackage is entirely defined in thestandard. These features are reframed on a common basis and the extension mechanism provides to the developers a way to include additional features in their GeoPackages.

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Geometry validation tools (3): FME

After discussing the ArcMap tool ( GIS tools for validating geometries (1) ) and the
tools Spatialite / PostGIS ( GIS tools for validating geometries (2): Spatialite and
we will discuss the available tools when using FME software
. The first two articles approached specific tools for a given format: ArcGis
shape and geodatabases, Spatialite databases or Postgis.

The FME tools, themselves, can process virtually all existing GIS formats.

First, just for once, FME documents the validation process by listing
the anomalies it takes into account . You will find a document in English with
a presentation of two options for validation and quality control on the
following page

Here we use the corresponding table for the validation of the geometries, but translated
in French. Since FME implements the GEOS definition, this table provides a
comprehension of the tests performed by the SQL queries in the Spatiality and
Postgis databases of the previous article.

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GIS tools for validating geometries (2): Spatialite and PostGis

In the previous article (GIS Tools for validating geometries (1)) we
processed the Italian Communes layer (com2011.shp) with the ArcMap geometry
checker. We did not detect any anomalies.

Now, let’s load this layer into a Spatialite database and see what we
find. As previously stated, this applies to a PostGIS database; the SQL queries
used being strictly the same.

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Change the name of a field in ArcGis: how to choose.

You have already been
faced with the problem of a field name that does not satisfy
you . But as soon
as data has been entered in the table it is no longer possible to modify the characteristics
of a field. The solution used is to create a new field with the desired characteristics, copy with the field calculator the contents of the old one
and then delete the old field from the table.

Not very elegant
or practical, several
solutions have been introduced in the latest
versions of ArcGis. The problem it is now to choose when changing the version.

Therefore, let’s discuss how to proceed according to
the version you are using.

Continue reading “Change the name of a field in ArcGis: how to choose.”

GIS tools for validating geometries (1)

Management and treatment algorithms for GIS data are developed with the
assumption that the geometry of the entities meets certain specifications. When
the data processing algorithms deal with data that does not respect these specifications,
the software can simply crash or, worse, the operation can succeed with no
apparent problem but the result is wrong. The subject is complicated since
there is almost no documentation as for what each software does. And if you
think that a control “Repair geometries” will remediate
this problem, you are far from reality …
At the origin of the wrong geometries; we find, basically, the ESRI shapefiles.
This quite old format (from the eighties) was not designed to incorporate the
topology constraints of a GIS. For example, two contiguous polygons can be
superimposed without problem , their boundaries can be double, there may be
empty spaces between the two limits , …
Unfortunately , it’s become a standard format for data exchange between
different GIS software , and even if all software publishers as well as the
OpenSource projects strive to propose alternative, powerful and much safer
management formats (ESRI geodatabase, PostGIS, Spatialite …) the users, most
often, opt for the ease of the shapefile solution.
But for those who opt for these current database formats, the problem is, only,
solved for the data created directly in these formats. When shapefiles
(shapefile) are loaded into ESRI geodatabases (personal or files), in a PostGis
database or Spatiality, etc., geometries are copied as they are, with all the
existing geometry problems. The same precaution and care must be taken when
using other formats where these data is imported.

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Starting with Geoserver

We have discussed how to start with Postgresql / Postgis. Once you have
your database, the next most common need is to upload online the data.

Of course, there are many technical possibilities to do this. To keep
within the most standard, the WFS and WMS streams setting from Postgresql /
Postgis data is one of the most robust ways.

Therefore, we will now see how to start with Geoserver.

NOTE: The original article was written for
Geoserver version 2.8.
I updated it on 9/9/2016 to take into account the installation
changes for version 2.9.1.

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