Define column types in a Dataset - Failure on append and Typesystem

Question

I have a basic function that populates a Dataset according to user specified parameters.

PopulateMap[eMapId_, eModule_, volBounds_, xInit_, yInit_, zInit_, \[CapitalDelta]x_, \[CapitalDelta]y_, \[CapitalDelta]z_] := 
Module[{eMap, segmentCount, segmentIndex, xPos, yPos, zPos},

      Remove[eMap];

      eMap = Dataset[{<|"MapId"->eMapId,
                        "ModuleId"->0,
                        "SegmentId"->0,
                        "x1"->0, "y1"->0, "z1"->0,
                        "x2"->0, "y2"->0, "z2"->0,
                         "Polarity"->0,
                         "ChargeDensity"->0|>}];

    segmentCount = Length[eModule];

    (* If passed eModule contains no segments *)    
    If[ segmentCount == 0, 
            Return[eMap]];

      xPos = xInit;
    yPos = yInit;
    zPos = zInit;

    While[ xPos < volBounds[1]["x2"],

        (* Add segments around {xPos, yPos, zPos} *)
        For[i=1, i<=segmentCount, i++,

            AppendTo[ eMap, <|"MapId"->eMapId,
                              "ModuleId"-> eModule[i]["ModuleId"], 
                              "SegmentId"->eModule[i]["SegmentId"],
                              "x1"->(xPos+eModule[i]["x1"]), 
                              "y1"->(yPos+eModule[i]["y1"]), 
                              "z1"->(zPos+eModule[i]["z1"]),
                              "x2"->(xPos+eModule[i]["x2"]), 
                              "y2"->(yPos+eModule[i]["y2"]), 
                              "z2"->(zPos+eModule[i]["z2"]),
                              "Polarity"->eModule[i]["Polarity"],
                              "ChargeDensity"->0|>]
        ];

        xPos += \[CapitalDelta]x;
        yPos += \[CapitalDelta]y;
        zPos += \[CapitalDelta]z;

      ];

    Return[eMap];
]

If I call PopulateMap with an integer for xInit (for example: -197):

eMap = PopulateMap[1, electrodeModule02, volumeBounds, -197, 0, 0, 20, 0, 0]

The Dataset is populated without problem.

If I set xInit to -197.5:

eMap = PopulateMap[1, electrodeModule02, volumeBounds, -197.5, 0, 0, 20, 0, 0]

The following error occurs:

Failure[Append, <|"MessageTemplate" :> Dataset::invalid, 
  "MessageParameters" -> <|"Head" -> Append, 
    "Arguments" -> {TypeSystem`Vector[
       TypeSystem`Assoc[TypeSystem`Atom[String], 
        TypeSystem`Atom[Integer], 11], 1]

Taking a queue from SQL-type languages I have used in the past, I made the following change to the first call to Dataset (changed the initial values for x1, y1, z1, x2, y2, z2 from 0 to 0.0:

          eMap = Dataset[{<|"MapId"->eMapId,
                        "ModuleId"->0,
                        "SegmentId"->0,
                        "x1"->0.0, "y1"->0.0, "z1"->0.0,
                        "x2"->0.0, "y2"->0.0, "z2"->0.0,
                         "Polarity"->0,
                         "ChargeDensity"->0|>}];

After this change, the Dataset is generated without error.

Is there a way to formally define the columns and column types in a Dataset? For example, if I wanted to store table definitions in an external file or database and instantiate the Datasets from the external definitions?